# offSchool

> offSchool is a simulation-first learning app for class 9–10 (SSC) students in Bangladesh. Every lesson follows the NCTB syllabus and starts with a real problem: the student predicts the answer, checks it by running a simulation, and only then learns the idea and its formula.

SSC Physics, Chemistry, Biology, Higher Mathematics, and Information and Communication Technology (ICT), every chapter and topic of the NCTB syllabus. Every page is in Bangla first; each simulation also has English text.

Key facts:
- Audience: class 9–10 (SSC) students in Bangladesh, in both the Bangla and English versions of the syllabus.
- Teaching loop: SSC Physics, Chemistry, Biology, Higher Math and ICT, with 252 simulations, clear notes, practice and an AI mentor. Bangla or English version, on any phone.
- Simulations: 252 published, each tied to a chapter and topic of the NCTB syllabus.
- Mentor: Ask any study question by typing it or photographing your notebook. The mentor finds the answer in the textbook, builds and runs a simulation step by step when that helps, and points out the step where your worked solution went wrong.
- Guardians: Most students are minors, so a parent or guardian needs to agree. At sign-up the student ticks the consent box to confirm it, no code or phone number needed. A parent can ask us to delete the account and all its data at any time.
- Status: offSchool opened to every student in October 2026 as a public beta. Every subject, simulation, note and practice set is ready to use; beta means we are still improving the app every week, so you may find a mistake now and then. Report it from any page and we fix it. Simulations, notes and practice stay free, and your progress is kept through every update.

## Pages

- [Home](https://offschool.site/): SSC Physics, Chemistry, Biology, Higher Math and ICT · discover ideas by playing simulations, in Bangla or English.
- [Subjects](https://offschool.site/subjects/): Every chapter and topic of five class 9–10 subjects, following the NCTB syllabus, with a simulation to play for each idea.
- [About offSchool](https://offschool.site/about/): who builds it, how lessons work, how the content is checked against the NCTB textbooks, and what the public beta means.
- [Plans and pricing](https://offschool.site/pricing/): Every offSchool simulation, note and practice set is free for everyone. Plans and monthly allowances for the AI mentor, khata checks and AI-marked answers.
- [Connect offSchool to Claude or ChatGPT](https://offschool.site/mcp/): offSchool is a remote MCP server (OAuth) at https://api.offschool.site/mcp with tools to search the SSC syllabus, read topic notes, find simulations, get formula sheets, practise with checked questions and see the student's own progress.
- [Guide: How to write and balance chemical equations, with examples](https://offschool.site/guides/balancing-chemical-equations/): Writing chemical equations: correct formulas from valency, the steps for balancing, nine worked examples, state symbols, and working out masses from an equation.
- [Guide: How to write electron configurations (with elements 1–30)](https://offschool.site/guides/electron-configuration-rules/): How to write an electron configuration: 2n², s p d f, the (n + l) rule, the Cr and Cu exceptions, a table for elements 1–30, and finding the period and group from it.
- [Guide: How to answer Higher Math creative questions](https://offschool.site/guides/higher-math-cq/): How to answer parts ক, খ and গ (2 + 4 + 4) of a Higher Math creative question: step marks, writing geometry and proofs, and one fully worked question.
- [Guide: How to find oxidation numbers (with KMnO₄ and K₂Cr₂O₇)](https://offschool.site/guides/oxidation-number-rules/): Finding oxidation numbers: the textbook's table of rules, a four-step method, worked answers to the book's "Do it yourself" set including KMnO₄, H₂SO₄ and K₂Cr₂O₇, and spotting redox.
- [Guide: How to remember the periodic table: elements 1–30 by rhyme](https://offschool.site/guides/periodic-table-mnemonics/): Bangla and English rhymes for the first 30 elements, rhymes for groups 1, 2, 17 and 18, symbols from Latin names, and practice drawing the table yourself.
- [Guide: How to solve physics numerical problems (six worked examples)](https://offschool.site/guides/physics-math-problems/): Six steps for physics numerical problems: the givens, unit conversion, formula, working and an answer with units, with worked examples on motion, force, work and power, pressure, heat and electricity.
- [Guide: SI units and dimensions: a list for SSC Physics](https://offschool.site/guides/si-units-and-dimensions/): The SI units of the seven base quantities, a table of units and dimensions for force, work, power, pressure and more, the prefix table, how to work out dimensions, and rules for writing units.
- [Guide: A plan for an A+ in SSC science: routine, MCQs and creative questions](https://offschool.site/guides/ssc-a-plus-plan/): A four-month plan for an A+ and GPA 5 in SSC science: a daily routine, tactics for MCQs and creative questions, practical exams, and common mistakes.
- [Guide: SSC 2027 science syllabus: the chapters of five subjects](https://offschool.site/guides/ssc-science-syllabus/): The chapters of SSC 2027 Physics, Chemistry, Biology, Higher Math and ICT, the main ideas in each, and a sensible order to study them in.
- [Guide: What is a creative question (CQ)? How to write parts ক, খ, গ and ঘ, with an example](https://offschool.site/guides/how-to-write-cq/): What a creative question (CQ) is, how its 10 marks are split across ক, খ, গ and ঘ, and how to write each part, with an SSC physics question showing which step of the answer earns each mark.

## Differences (পার্থক্য)

- [All comparisons](https://offschool.site/compare/): The differences the board exam asks again and again, as tables and plain explanations, each with a simulation and practice questions.
- [Concave mirror and Convex mirror (অবতল দর্পণ ও উত্তল দর্পণ)](https://offschool.site/compare/concave-vs-convex-mirror/): Concave and convex mirrors compared: reflecting surface, converging or diverging, the images they form and their uses. Why a car's side mirror is convex; SSC Physics.
- [Alpha rays (α), Beta rays (β) and Gamma rays (γ) (আলফা রশ্মি (α), বিটা রশ্মি (β) ও গামা রশ্মি (γ))](https://offschool.site/compare/alpha-beta-gamma-rays/): Alpha, beta and gamma rays in one table: nature, charge, penetrating and ionising power, what stops them and what changes in the nucleus. From the radioactivity part of SSC Physics.
- [Reflection of light and Refraction of light (আলোর প্রতিফলন ও আলোর প্রতিসরণ)](https://offschool.site/compare/reflection-vs-refraction/): Reflection and refraction of light compared: medium, speed, direction, laws and examples. Why a straw in water looks bent; from the SSC Physics chapters on light.
- [Convex lens and Concave lens (উত্তল লেন্স ও অবতল লেন্স)](https://offschool.site/compare/concave-vs-convex-lens/): Convex and concave lenses compared: shape, converging or diverging, images, the sign of their power and their use in spectacles, including short and long sight. SSC Physics.
- [AC and DC (এসি (AC) ও ডিসি (DC))](https://offschool.site/compare/ac-vs-dc/): AC and DC compared: direction, source, symbol, whether a transformer works with it, and uses. Why homes get AC; from the SSC Physics electricity chapters.
- [Work, Energy and Power (কাজ, শক্তি ও ক্ষমতা)](https://offschool.site/compare/work-energy-power/): Work, energy and power in one table: definitions, formulas, units and examples, with a porter lifting a sack worked through. From the SSC Physics chapter on work, power and energy.
- [Kinetic energy and Potential energy (গতিশক্তি ও বিভব বা স্থিতিশক্তি)](https://offschool.site/compare/kinetic-vs-potential-energy/): Kinetic and potential energy compared: why an object has each, formulas, what each depends on, and examples, with the energy changes on a slide. From SSC Physics.
- [Heat and Temperature (তাপ ও তাপমাত্রা)](https://offschool.site/compare/heat-vs-temperature/): Heat and temperature compared: what each is, unit, how it is measured, whether it depends on mass. With a bucket of warm water against a cup of boiling water; SSC Physics.
- [Distance and Displacement (দূরত্ব ও সরণ)](https://offschool.site/compare/distance-vs-displacement/): Distance and displacement compared: scalar or vector, whether it depends on the path, whether it can be zero. With a walk-to-school example and simulation; SSC Physics.
- [Speed and Velocity (দ্রুতি ও বেগ)](https://offschool.site/compare/speed-vs-velocity/): Speed and velocity compared: scalar or vector, formula, unit, whether it can be negative. Why velocity changes on a circular path; from SSC Physics, motion.
- [Nuclear fission and Nuclear fusion (নিউক্লীয় ফিশন ও নিউক্লীয় ফিউশন)](https://offschool.site/compare/fission-vs-fusion/): Nuclear fission and fusion compared at SSC level: what happens, the fuel, where each is found and whether it is used today, with Rooppur and the sun as examples.
- [Conductor, Insulator and Semiconductor (পরিবাহী, অপরিবাহী ও অর্ধপরিবাহী)](https://offschool.site/compare/conductor-insulator-semiconductor/): Conductors, insulators and semiconductors in one table: free electrons, the effect of temperature, examples and uses. Why wires are covered in plastic; SSC Physics.
- [Evaporation and Boiling (বাষ্পায়ন ও স্ফুটন)](https://offschool.site/compare/evaporation-vs-boiling/): Evaporation and boiling compared: at what temperature, from where in the liquid, how fast, and whether it cools. Why water in a clay pot stays cool; from SSC Physics.
- [Mass and Weight (ভর ও ওজন)](https://offschool.site/compare/mass-vs-weight/): Mass and weight compared: definition, unit, scalar or vector, and whether it changes from place to place, with W = mg. From the SSC Physics chapter on force.
- [Electric motor and Generator (বৈদ্যুতিক মোটর ও জেনারেটর)](https://offschool.site/compare/motor-vs-generator/): Motors and generators compared: energy change, principle, what goes into the coil and what comes out, and uses, with a bicycle dynamo. From SSC Physics.
- [Series connection and Parallel connection (শ্রেণি সংযোগ ও সমান্তরাল সংযোগ)](https://offschool.site/compare/series-vs-parallel-circuit/): Series and parallel connections compared: current, potential difference, equivalent-resistance formulas and uses. Why home lights are in parallel, with three simulations; SSC Physics.
- [Scalar quantity and Vector quantity (স্কেলার রাশি ও ভেক্টর রাশি)](https://offschool.site/compare/scalar-vs-vector/): Scalars and vectors compared: direction, how they add, how they are written, with lists of examples, and an easy way to tell them apart. From SSC Physics.
- [Orbit (main energy level) and Orbital (sublevel) (কক্ষপথ (প্রধান শক্তিস্তর) ও অরবিটাল (উপশক্তিস্তর))](https://offschool.site/compare/orbit-vs-orbital/): Orbits (main energy levels) and orbitals (sublevels) compared in the SSC Chemistry book's own terms: n and l, K L M N versus s p d f, 2n² and 2(2l+1) electrons.
- [Molecular formula and Empirical formula (আণবিক সংকেত ও স্থূল সংকেত)](https://offschool.site/compare/molecular-vs-empirical-formula/): Molecular and empirical formulas compared: what each shows, how they relate, when they are the same, and examples, with a worked empirical formula from percentage composition. SSC Chemistry, mole concept.
- [Ionic bond and compounds and Covalent bond and compounds (আয়নিক বন্ধন ও যৌগ ও সমযোজী বন্ধন ও যৌগ)](https://offschool.site/compare/ionic-vs-covalent-bond/): Ionic and covalent bonds and compounds compared: transfer or sharing of electrons, melting point, solubility in water, conducting electricity, with the salt-versus-sugar test. SSC Chemistry.
- [Acid and Alkali (এসিড (অম্ল) ও ক্ষার)](https://offschool.site/compare/acid-vs-alkali/): Acids and alkalis compared: taste, litmus and indicators, pH, which ions they give in water, and examples, with a way to test kitchen items. SSC Chemistry.
- [Solid, Liquid and Gas (কঠিন, তরল ও গ্যাস)](https://offschool.site/compare/solid-liquid-gas/): Solids, liquids and gases in one table: shape, volume, spacing, attraction and movement of particles, explained by the kinetic particle theory, with a naphthalene simulation. SSC Chemistry.
- [Base and Alkali (ক্ষারক ও ক্ষার)](https://offschool.site/compare/base-vs-alkali/): Bases and alkalis compared: definition, solubility in water, form and examples. Why every alkali is a base but not every base is an alkali, as the SSC Chemistry topic teaches it.
- [Oxidation and Reduction (জারণ ও বিজারণ)](https://offschool.site/compare/oxidation-vs-reduction/): Oxidation and reduction compared by electrons, oxidation number, oxygen and hydrogen, with how to spot the oxidising and reducing agents and a copper-silver simulation. SSC Chemistry.
- [Oxidation number and Valency (জারণ সংখ্যা ও যোজনী (যোজ্যতা))](https://offschool.site/compare/oxidation-number-vs-valency/): Oxidation number and valency compared: what each means, sign, whether it can be zero or a fraction, with examples. Why they are not the same, explained; SSC Chemistry.
- [Solute and Solvent (দ্রব ও দ্রাবক)](https://offschool.site/compare/solute-vs-solvent/): Solute, solvent and solution compared: which is which, amounts, state and examples, with salt water and sherbet, leading into molar solutions. SSC Chemistry.
- [Metal and Non-metal (ধাতু ও অধাতু)](https://offschool.site/compare/metal-vs-nonmetal/): Metals and non-metals compared: lustre, conductivity, malleability, giving or taking electrons, the nature of their oxides, with examples and the exceptions mercury and graphite. SSC Chemistry.
- [Atom and Molecule (পরমাণু ও অণু)](https://offschool.site/compare/atom-vs-molecule/): Atoms and molecules compared: definition, whether they exist freely, bonds, whether they can be divided, with examples. Why O and O₂ differ; from SSC Chemistry, structure of matter.
- [Atomic number (Z) and Mass number (A) (পারমাণবিক সংখ্যা (Z) ও ভর সংখ্যা (A))](https://offschool.site/compare/atomic-number-vs-mass-number/): Atomic number and mass number compared: what each counts, the symbols, whether it identifies the element, and what happens in isotopes, with how to find the number of neutrons. SSC Chemistry.
- [Diffusion and Effusion (ব্যাপন ও নিঃসরণ)](https://offschool.site/compare/diffusion-vs-effusion/): Diffusion and effusion compared: what happens, whether a hole is needed, in which media, particle collisions and examples, with the ammonia and HCl white-smoke simulation. SSC Chemistry.
- [Physical change and Chemical change (ভৌত পরিবর্তন ও রাসায়নিক পরিবর্তন)](https://offschool.site/compare/physical-vs-chemical-change/): Physical and chemical changes compared: new substances, whether they can be reversed, energy changes and examples. Why melting wax and burning wax differ, with a simulation. SSC Chemistry.
- [Element, Compound and Mixture (মৌল (মৌলিক পদার্থ), যৌগ (যৌগিক পদার্থ) ও মিশ্রণ)](https://offschool.site/compare/element-compound-mixture/): Elements, compounds and mixtures in one table: make-up, proportions, properties, how to separate them, and examples. Why water is a compound and air a mixture; SSC Chemistry.
- [Saturated hydrocarbons (alkanes) and Unsaturated hydrocarbons (alkenes, alkynes) (সম্পৃক্ত হাইড্রোকার্বন (অ্যালকেন) ও অসম্পৃক্ত হাইড্রোকার্বন (অ্যালকিন, অ্যালকাইন))](https://offschool.site/compare/saturated-vs-unsaturated-hydrocarbon/): Saturated and unsaturated hydrocarbons compared: bonds, general formula, reactivity, the bromine water test, flame and examples, including alkanes and alkenes. SSC Chemistry.
- [Plant cell and Animal cell (উদ্ভিদ কোষ ও প্রাণিকোষ)](https://offschool.site/compare/plant-cell-vs-animal-cell/): Plant and animal cells compared in a table: cell wall, plastids, vacuole, centrosome and shape. From the SSC Biology chapter on cells and tissues.
- [Food chain and Food web (খাদ্যশৃঙ্খল ও খাদ্যজাল)](https://offschool.site/compare/food-chain-vs-food-web/): Food chains and food webs compared: structure, food pathways, stability and examples. Why an ecosystem lasts better with a web; from SSC Biology.
- [Xylem and Phloem (জাইলেম ও ফ্লোয়েম)](https://offschool.site/compare/xylem-vs-phloem/): Xylem and phloem compared: what each carries, which way, whether its cells are living or dead, and what it is made of. From the SSC Biology chapter on tissues.
- [Gene and Chromosome (জিন ও ক্রোমোজোম)](https://offschool.site/compare/gene-vs-chromosome/): Genes and chromosomes compared: what each is, where it is, size, number and job. Which is the unit of heredity and which its physical basis; from SSC Biology.
- [DNA and RNA (ডিএনএ (DNA) ও আরএনএ (RNA))](https://offschool.site/compare/dna-vs-rna/): DNA and RNA compared in a table: strands, sugar, bases, where they are and what they do. From the SSC Biology chapter on heredity, with a simulation and MCQs.
- [Artery and Vein (ধমনি ও শিরা)](https://offschool.site/compare/artery-vs-vein/): Arteries and veins compared: direction of blood, oxygen, walls, valves and pulse, including the pulmonary exceptions. From SSC Biology.
- [Prokaryotic cell and Eukaryotic cell (প্রোক্যারিওটিক কোষ ও ইউক্যারিওটিক কোষ)](https://offschool.site/compare/prokaryotic-vs-eukaryotic-cell/): Prokaryotic and eukaryotic cells compared: nuclear membrane, organelles, division and examples. From the classification part of SSC Biology.
- [Diffusion and Osmosis (ব্যাপন ও অভিস্রবণ)](https://offschool.site/compare/diffusion-vs-osmosis/): Diffusion and osmosis compared: what moves, whether a membrane is needed and which way it goes. Why osmosis is a special kind of diffusion, with a potato simulation and MCQs.
- [Mitosis and Meiosis (মাইটোসিস ও মিয়োসিস)](https://offschool.site/compare/mitosis-vs-meiosis/): Mitosis and meiosis compared in a table: where each happens, how many cells form, what happens to the chromosome number, and why each matters. From SSC Biology, cell division.
- [Blood and Lymph (রক্ত ও লসিকা)](https://offschool.site/compare/blood-vs-lymph/): Blood and lymph compared: colour, cells, route and job. Both are fluid connective tissues, yet they differ; from SSC Biology.
- [Red blood cell (RBC) and White blood cell (WBC) (লোহিত রক্তকণিকা (RBC) ও শ্বেত রক্তকণিকা (WBC))](https://offschool.site/compare/red-vs-white-blood-cells/): Red and white blood cells compared: nucleus, colour, number, lifespan and job, with the textbook's figures. From the SSC Biology chapter on transport in organisms.
- [Aerobic respiration and Anaerobic respiration (সবাত শ্বসন ও অবাত শ্বসন)](https://offschool.site/compare/aerobic-vs-anaerobic-respiration/): Aerobic and anaerobic respiration compared: oxygen, where it happens, how far glucose is broken down, how much ATP and what is produced. From SSC Biology, bioenergetics.
- [Photosynthesis and Respiration (সালোকসংশ্লেষণ ও শ্বসন)](https://offschool.site/compare/photosynthesis-vs-respiration/): Photosynthesis and respiration compared: where they happen, what goes in and out, and whether energy is stored or released, with both equations. From SSC Biology, bioenergetics.
- [C₃ plants and C₄ plants (C₃ উদ্ভিদ ও C₄ উদ্ভিদ)](https://offschool.site/compare/c3-vs-c4-plants/): C3 and C4 plants compared: the first stable compound, which cycles run, the rate of photosynthesis and examples. Why maize is a C4 plant; from SSC Biology.
- [Sequence and Series (অনুক্রম ও ধারা)](https://offschool.site/compare/sequence-vs-series/): Sequences and series compared: what each is, how it is written, whether it has a sum, with examples and the condition for an infinite geometric series to have a sum. SSC Higher Math.
- [Relation and Function (অন্বয় ও ফাংশন)](https://offschool.site/compare/relation-vs-function/): Relations and functions compared: definition, how many images each element has, ordered pairs and examples, with how to tell which relation is not a function. SSC Higher Math.
- [Subset and Proper subset (উপসেট ও প্রকৃত উপসেট)](https://offschool.site/compare/subset-vs-proper-subset/): Subsets and proper subsets compared: definition, the symbols ⊆ and ⊂, whether a set counts, how many there are (2ⁿ and 2ⁿ − 1), the empty set and examples. SSC Higher Math.
- [Degree (sexagesimal system) and Radian (circular system) (ডিগ্রি (ষাটমূলক পদ্ধতি) ও রেডিয়ান (বৃত্তীয় পদ্ধতি))](https://offschool.site/compare/degree-vs-radian/): Degrees and radians compared: the sexagesimal and circular systems, how each unit is defined, symbols, s = rθ and how to convert, from π radians = 180°. SSC Higher Math.
- [Equation and Identity (সমীকরণ ও অভেদ)](https://offschool.site/compare/equation-vs-identity/): Equations and identities compared: when each is true, the sign, solutions, matching coefficients and examples, with why identities matter for partial fractions. SSC Higher Math.
- [Web page, Website and Web portal (ওয়েব পেইজ, ওয়েবসাইট ও ওয়েব পোর্টাল)](https://offschool.site/compare/webpage-website-portal/): Web pages, websites and web portals compared: what each is, what it is made of, what it holds and examples, including Bangladesh's national information portal. SSC ICT.
- [Web server and Web client (ওয়েব সার্ভার ও ওয়েব ক্লায়েন্ট)](https://offschool.site/compare/web-server-vs-web-client/): Web servers and web clients compared: who sends the request, who sends the response, HTTP/HTTPS, how many each serves, with examples. SSC ICT.
- [Compiler and Interpreter (কম্পাইলার ও ইন্টারপ্রেটার)](https://offschool.site/compare/compiler-vs-interpreter/): Compilers and interpreters compared: how each turns code into machine code, what happens on an error, speed and examples, and why Python uses an interpreter. SSC ICT.
- [Download and Upload (ডাউনলোড ও আপলোড)](https://offschool.site/compare/download-vs-upload/): Downloading and uploading compared: which way the data goes, from where to where, where it ends up, with everyday examples such as email and videos. SSC ICT.
- [Preventive maintenance and Corrective maintenance (প্রতিরোধমূলক রক্ষণাবেক্ষণ ও সংশোধনমূলক রক্ষণাবেক্ষণ)](https://offschool.site/compare/preventive-vs-corrective-maintenance/): Preventive and corrective computer maintenance compared: when each is done, who does it, cost and examples, from virus scans to repairs. SSC ICT.
- [Uninstall and Delete (আনইনস্টল ও ডিলিট)](https://offschool.site/compare/uninstall-vs-delete/): Uninstalling and deleting software compared in the SSC ICT book's own terms: what each removes, what stays in the registry, which comes first, the steps and the care needed.
- [break statement and continue statement (break স্টেটমেন্ট ও continue স্টেটমেন্ট)](https://offschool.site/compare/break-vs-continue/): The break and continue statements in Python compared: what happens to the loop, whether later passes run, and examples with their output, plus how to tell which numbers get skipped. SSC ICT.
- [for loop and while loop (for লুপ ও while লুপ)](https://offschool.site/compare/for-vs-while-loop/): for and while loops in Python compared: when to use each, the counter, checking the condition, range() and the risk of an endless loop, with one task written both ways. SSC ICT.

## Platform comparisons

- [All platform comparisons](https://offschool.site/vs/): The online platforms SSC science students use, side by side: what each teaches, how, what it costs and who it suits best. Every fact has its source and the date we checked it.
- [Online platforms for SSC science: 7 compared (2026)](https://offschool.site/vs/ssc-online-platforms/): 10 Minute School, Shikho, Udvash, Chorcha, Borno AI, ACS and offSchool side by side: live classes, video, simulations, AI, practice and prices, with sources. (facts checked 2026-10-22)
- [offSchool vs 10 Minute School for SSC science](https://offschool.site/vs/offschool-vs-10-minute-school/): offSchool and 10 Minute School for SSC science side by side: live classes, video, simulations, AI, practice, versions and price, with sources and dates. (facts checked 2026-10-22)
- [offSchool vs Borno AI: AI tutor and simulations compared](https://offschool.site/vs/offschool-vs-borno-ai/): offSchool and Borno AI (borno.ai) side by side: AI tutor, labs and simulations, MCQ/CQ, classes covered, versions, apps and price, with sources. (facts checked 2026-10-22)
- [offSchool vs Chorcha for SSC science: practice and price](https://offschool.site/vs/offschool-vs-chorcha/): offSchool and Chorcha side by side: question bank, mock tests, simulations, notes, AI, versions and price. Is Chorcha free, and who suits which, with sources. (facts checked 2026-10-22)
- [offSchool vs Shikho for SSC science: differences and price](https://offschool.site/vs/offschool-vs-shikho/): offSchool and Shikho for SSC science side by side: live classes, animated videos versus simulations, AI, exams, versions and price, with sources. (facts checked 2026-10-22)
- [offSchool vs Udvash-Unmesh for SSC science](https://offschool.site/vs/offschool-vs-udvash/): offSchool and Udvash-Unmesh for SSC science side by side: online classes, branches, exams, teachers' Q&A, simulations, versions and price, with sources. (facts checked 2026-10-22)
- [10 Minute School vs Udvash: SSC preparation compared](https://offschool.site/vs/10-minute-school-vs-udvash/): 10 Minute School and Udvash-Unmesh for SSC science side by side: live classes, marked exams, AI versus teachers' Q&A, versions, branches and price, with sources. (facts checked 2026-10-22)
- [Shikho vs 10 Minute School: which is better for SSC?](https://offschool.site/vs/shikho-vs-10-minute-school/): Shikho and 10 Minute School SSC science batches side by side: live classes, videos, exams, AI, versions, apps and price. Who suits which, with dated sources. (facts checked 2026-10-22)
- [Udvash vs Shikho for SSC science: who suits which](https://offschool.site/vs/udvash-vs-shikho/): Udvash-Unmesh and Shikho for SSC science side by side: coaching versus online, classes, marked exams, teachers versus AI, versions and price, with sources. (facts checked 2026-10-22)

## Physics (পদার্থবিজ্ঞান)

Measurement, motion, force, energy, heat, pressure, waves and sound, light, electricity, magnetism and modern physics, run every idea as a simulation.

- [SSC Physics](https://offschool.site/subjects/physics/): পরিমাপ, গতি, বল, শক্তি, তাপ, চাপ, তরঙ্গ ও শব্দ, আলো, তড়িৎ, চুম্বকত্ব আর আধুনিক পদার্থবিজ্ঞান, প্রতিটি ধারণা সিমুলেশনে চালিয়ে দেখো।
- [SSC Physics formula sheet](https://offschool.site/subjects/physics/formulas/): every formula, chapter by chapter, each with its simulation.
- [Chapter 1: Physical Quantities and Their Measurements (ভৌত রাশি এবং তাদের পরিমাপ)](https://offschool.site/subjects/physics/ch01/)
  - [Topic: Physics (পদার্থবিজ্ঞান)](https://offschool.site/subjects/physics/ch01/t01/)
  - [Topic: Objectives of physics (পদার্থবিজ্ঞানের উদ্দেশ্য)](https://offschool.site/subjects/physics/ch01/t02/)
  - [Topic: The foundation of science education: magnitudes and units of physical quantities (বিজ্ঞান শিক্ষার ভিত্তি: ভৌত রাশির মান ও একক)](https://offschool.site/subjects/physics/ch01/t04/)
  - [Topic: Units of measurement and their necessity (পরিমাপের একক ও প্রয়োজনীয়তা)](https://offschool.site/subjects/physics/ch01/t05/)
  - [Topic: Fundamental and derived quantities and their units (মৌলিক রাশি এবং লব্ধ রাশি এবং এদের একক)](https://offschool.site/subjects/physics/ch01/t06/)
  - [Topic: International System of Units (পরিমাপের আন্তর্জাতিক একক)](https://offschool.site/subjects/physics/ch01/t07/)
  - [Topic: Dimensions of quantities (রাশির মাত্রা)](https://offschool.site/subjects/physics/ch01/t08/)
  - [Topic: Use of prefixes (multiples and submultiples) (উপসর্গের ব্যবহার (গুণিতক ও উপগুণিতক))](https://offschool.site/subjects/physics/ch01/t09/)
  - [Topic: Use of standard form (scientific notation) (আদর্শ রূপ বা বৈজ্ঞানিক প্রতীকের ব্যবহার)](https://offschool.site/subjects/physics/ch01/t10/)
  - [Topic: Measuring instruments (পরিমাপের যন্ত্রপাতি)](https://offschool.site/subjects/physics/ch01/t11/)
  - [Topic: Errors in measurement (পরিমাপে ত্রুটি (Error))](https://offschool.site/subjects/physics/ch01/t12/)
  - [Topic: Techniques for maintaining accuracy, precision and sensitivity in measurement (পরিমাপে যথার্থতা, নির্ভুলতা ও সূক্ষ্মমান বজায় রাখার কৌশল)](https://offschool.site/subjects/physics/ch01/t13/)
  - [Simulation: From the Padma Bridge to a blood cell: which unit? (পদ্মা সেতু থেকে রক্তকণিকা: কোন এককে লিখবে?)](https://offschool.site/sim/ssc.physics.ch01.bridge-to-blood-cell/): The Padma Bridge is 6150 metres long, and a red blood cell is just 7 micrometres across. To write such huge and tiny numbers side by side, scientists use prefixes and standard form (a × 10ⁿ). What is 7 µm in metres, in standard form?
  - [Simulation: Tanti Bazar goldsmith and the finer vernier (তাঁতীবাজারের স্বর্ণকার ও সূক্ষ্মতর ভার্নিয়ার)](https://offschool.site/sim/ssc.physics.ch01.goldsmith-finer-vernier/): A goldsmith in Tanti Bazar must measure a gold bangle's thickness down to 0.02 mm. But the school vernier caliper has a 1 mm main scale and 10 vernier divisions, reading only to 0.1 mm. If the bangle's true thickness is 12.34 mm, how can the caliper's design be changed to bring measurement error down to zero?
  - [Simulation: Nawabpur earthing wire and screw gauge (নবাবপুরের আর্থিং তার ও স্ক্রু গজ)](https://offschool.site/sim/ssc.physics.ch01.screw-gauge-earth-wire/): An electrician in Nawabpur is choosing copper earthing wire and needs its diameter measured to 0.01 mm, which a ruler or vernier cannot provide. He picks a screw gauge with a pitch of 0.5 mm and 50 circular scale divisions. What is the smallest length this gauge can measure accurately?
  - [Simulation: Vernier caliper reading and zero error (স্লাইড ক্যালিপার্সের পাঠ ও যান্ত্রিক ত্রুটি)](https://offschool.site/sim/ssc.physics.ch01.vernier-reading/): A vernier caliper is used to measure the diameter of a pencil. When the jaws are closed before measuring, the vernier zero sits to the left of the main scale zero, meaning the instrument has a negative zero error of -0.2 mm. Clamping the pencil gives a main scale reading of 7 mm and a vernier coincidence of 6 (least count 0.1 mm), resulting in an observed reading of 7.6 mm. What is the actual diameter of the pencil?
  - [Simulation: What is a newton made of? (নিউটন আসলে কী দিয়ে তৈরি?)](https://offschool.site/sim/ssc.physics.ch01.what-is-a-newton/): Sakib knows that length, mass and time are base quantities, and that velocity (length ÷ time) is a derived quantity built from them. Force = mass × acceleration, measured in newtons. In terms of mass (M), length (L) and time (T), what is the dimension of force?
- [Chapter 2: Motion (গতি)](https://offschool.site/subjects/physics/ch02/)
  - [Topic: Rest and motion (স্থিতি এবং গতি)](https://offschool.site/subjects/physics/ch02/t01/)
  - [Topic: Different types of motion (বিভিন্ন প্রকার গতি)](https://offschool.site/subjects/physics/ch02/t02/)
  - [Topic: Scalar and vector quantities (স্কেলার ও ভেক্টর রাশি)](https://offschool.site/subjects/physics/ch02/t03/)
  - [Topic: Quantities of motion and their mathematical relations (গতি সংশ্লিষ্ট রাশি এবং এদের গাণিতিক সম্পর্ক)](https://offschool.site/subjects/physics/ch02/t04/)
  - [Topic: Motion of freely falling bodies: acceleration due to gravity (মুক্তভাবে পড়ন্ত বস্তুর গতি: অভিকর্ষজ ত্বরণ)](https://offschool.site/subjects/physics/ch02/t05/)
  - [Topic: Analysis of motion with the help of graphs (লেখচিত্রের সাহায্যে গতি বিশ্লেষণ)](https://offschool.site/subjects/physics/ch02/t06/)
  - [Simulation: A Ball Thrown Straight Up: How High Does It Go? (খাড়া উপরে ছোড়া বল: কত উঁচুতে উঠবে?)](https://offschool.site/sim/ssc.physics.ch02.ball-thrown-straight-up/): A player on a field throws a ball straight up at 20 m/s. Take the ball to leave from ground level and ignore air resistance. How high does the ball rise, and after how long does it come back down to the ground?
  - [Simulation: Free fall of a jackfruit (মুক্তভাবে পড়ন্ত কাঁঠাল)](https://offschool.site/sim/ssc.physics.ch02.jackfruit-free-fall/): In a Gazipur orchard, a ripe jackfruit drops from a 19.6 m branch and hits the ground after 2 s. If the branch were four times higher, at 78.4 m, how long would it take to reach the ground?
  - [Simulation: Speeding up from rest (স্থির অবস্থা থেকে বেগ বাড়ানো)](https://offschool.site/sim/ssc.physics.ch02.rickshaw-acceleration/): An e-rickshaw starts from rest and gains 2 m/s of speed every second. In the first 2 seconds it covers 4 m. How far will it have gone after 4 seconds?
  - [Simulation: Swing at Ramna Park: what changes the period? (রমনা পার্কের দোলনা: দোলনকাল কীসের ওপর নির্ভর করে?)](https://offschool.site/sim/ssc.physics.ch02.swing-pendulum-period/): A child is swinging on a swing at Ramna Park. The time it takes to swing forward and return to the starting position is called the period. If a heavier child sits on the swing, or if the rope length is increased, which change will make one full swing take the longest time?
  - [Simulation: Is the train next to you moving or still? (পাশের ট্রেনটি চলছে, না দাঁড়িয়ে?)](https://offschool.site/sim/ssc.physics.ch02.two-trains-at-kamalapur/): Two trains leave Kamalapur side by side, going the same way at 60 km/h. From a window of train A, Mitu looks at a passenger in train B. How does train B seem to Mitu?
  - [Simulation: Walk to school: distance and displacement (বিদ্যালয়ে যাওয়ার পথ: দূরত্ব ও সরণ)](https://offschool.site/sim/ssc.physics.ch02.walk-to-school-displacement/): To walk from home to school around a pond in Rajshahi, Nila goes 300 m straight east, then 400 m straight north. On a grid where each unit represents 100 m, these legs are vectors a = (3, 0) and b = (0, 4). What is the straight-line displacement from home to school?
- [Chapter 3: Force (বল)](https://offschool.site/subjects/physics/ch03/)
  - [Topic: Inertia and the qualitative concept of force: Newton's first law (জড়তা এবং বলের গুণগত ধারণা: নিউটনের প্রথম সূত্র)](https://offschool.site/subjects/physics/ch03/t01/)
  - [Topic: Nature of the fundamental forces (মৌলিক বলের প্রকৃতি)](https://offschool.site/subjects/physics/ch03/t02/)
  - [Topic: Balanced and unbalanced forces (সাম্যতা ও সাম্যতাবিহীন বল (Balanced & Unbalanced Forces))](https://offschool.site/subjects/physics/ch03/t03/)
  - [Topic: Momentum and collision (ভরবেগ এবং সংঘর্ষ)](https://offschool.site/subjects/physics/ch03/t04/)
  - [Topic: Effect of force on motion (গতির উপর বলের প্রভাব)](https://offschool.site/subjects/physics/ch03/t05/)
  - [Topic: Relation between force and acceleration: Newton's second law (বল এবং ত্বরণের সম্পর্ক: নিউটনের দ্বিতীয় সূত্র)](https://offschool.site/subjects/physics/ch03/t06/)
  - [Topic: Gravitational force (মহাকর্ষ বল)](https://offschool.site/subjects/physics/ch03/t13/)
  - [Topic: Action and reaction forces: Newton's third law (ক্রিয়া ও প্রতিক্রিয়া বল: নিউটনের তৃতীয় সূত্র)](https://offschool.site/subjects/physics/ch03/t07/)
  - [Topic: Safe travel: motion and force (নিরাপদ ভ্রমণ: গতি ও বল)](https://offschool.site/subjects/physics/ch03/t08/)
  - [Topic: Friction and its types (ঘর্ষণ ও এর প্রকারভেদ)](https://offschool.site/subjects/physics/ch03/t09/)
  - [Topic: Effect of friction on motion (গতির উপর ঘর্ষণের প্রভাব)](https://offschool.site/subjects/physics/ch03/t10/)
  - [Topic: Increasing and decreasing friction (ঘর্ষণের হ্রাস বৃদ্ধি (Increasing and Decreasing Friction))](https://offschool.site/subjects/physics/ch03/t11/)
  - [Topic: Friction: a necessary evil (ঘর্ষণ: একটি অপরিহার্য অমঙ্গল)](https://offschool.site/subjects/physics/ch03/t12/)
  - [Simulation: Pushing a luggage trolley: force and acceleration (লাগেজ ট্রলি ঠেলা: বল ও ত্বরণ)](https://offschool.site/sim/ssc.physics.ch03.airport-trolley-push/): On the smooth floor of Shahjalal International Airport, a luggage trolley of total mass 50 kg is pushed with a 100 N horizontal force. Since friction is negligible, the trolley moves forward with an acceleration of 2 m/s². More luggage is then loaded, doubling the total mass to 100 kg. If the passenger continues to push with the same 100 N force, what will the new acceleration be?
  - [Simulation: Pushing an almirah on the floor: limiting friction (মেঝেতে আলমারি ঠেলা: সীমাস্ত ঘর্ষণ)](https://offschool.site/sim/ssc.physics.ch03.almirah-friction-push/): A heavy steel almirah of mass 60 kg rests on a tiled home floor. The friction coefficient between the almirah and the floor is μ = 0.4. A horizontal push of 200 N is applied to move it (with g = 9.8 m/s²). Will the almirah move?
  - [Simulation: Boatman pushes off: action and reaction (লগি দিয়ে নৌকা ঠেলা: ক্রিয়া ও প্রতিক্রিয়া)](https://offschool.site/sim/ssc.physics.ch03.boatman-pushes-off/): At Sadarghat on the Buriganga river, a boatman in boat A pushes an adjacent boat B away with a pole, applying a 200 N force for 0.5 s. With boatman and cargo, boat A has a mass of 400 kg, while empty boat B has a mass of 200 kg. If water friction is negligible, which boat moves faster after the push?
  - [Simulation: Bus brakes: why do passengers lean forward? (বাসে ব্রেক: যাত্রী কেন সামনে ঝুঁকে পড়েন?)](https://offschool.site/sim/ssc.physics.ch03.bus-brakes-passenger/): A local bus on Mirpur Road in Dhaka is moving at a uniform velocity of 6 m/s with a standing passenger. A pedestrian suddenly steps ahead, and the driver applies a 3000 N braking force to stop the bus. If rainwater and soap make the bus floor completely slippery and frictionless (μ = 0), what will the passenger's velocity be after the bus stops?
  - [Simulation: Safe travel: braking distance (নিরাপদ ভ্রমণ: ব্রেকিং দূরত্ব)](https://offschool.site/sim/ssc.physics.ch03.highway-braking-distance/): A bus on the Dhaka-Mawa expressway travels at 10 m/s and brakes with a deceleration of 5 m/s², stopping in 10 m. If the bus was travelling twice as fast at 20 m/s, what distance would it need to stop at the same deceleration?
  - [Simulation: Rickshaw van on a slope and friction (ঢালু পথে রিকশাভ্যান ও ঘর্ষণ)](https://offschool.site/sim/ssc.physics.ch03.rickshaw-on-a-slope/): A loaded rickshaw van of mass 100 kg is parked on a flyover slope. The coefficient of friction between the tyres and the road is μ = 0.577 (where tan(30°) ≈ 0.577). Currently, at a slope angle of 15°, the van stays safely at rest. As the slope angle increases, at what angle will the van overcome friction and begin sliding down?
  - [Simulation: Trolley crash: where does the momentum go? (ট্রলির ধাক্কা: ভরবেগ কোথায় যায়?)](https://offschool.site/sim/ssc.physics.ch03.trolley-collision/): At Kamalapur station a loaded trolley rolls at 2 m/s into an identical trolley standing still on the platform. After the crash the first trolley slows down and the second starts moving. Is some momentum lost in the crash, or does it only move from one trolley to the other?
- [Chapter 4: Work, Power and Energy (কাজ, ক্ষমতা ও শক্তি)](https://offschool.site/subjects/physics/ch04/)
  - [Topic: Work and energy (কাজ ও শক্তি)](https://offschool.site/subjects/physics/ch04/t01/)
  - [Topic: Kinetic energy and potential energy and their calculation (গতি শক্তি ও স্থিতি শক্তি এবং এদের গাণিতিক হিসাব)](https://offschool.site/subjects/physics/ch04/t02/)
  - [Topic: Main sources of energy and the transformation of energy (শক্তির প্রধান উৎস এবং শক্তির রূপান্তর)](https://offschool.site/subjects/physics/ch04/t03/)
  - [Topic: Transformation of energy and the principle of conservation of energy (শক্তির রূপান্তর এবং শক্তির নিত্যতা বা সংরক্ষণশীলতার নীতি)](https://offschool.site/subjects/physics/ch04/t04/)
  - [Topic: Transformation and use of energy and their effect on the environment (শক্তির রূপান্তর, ব্যবহার এবং পরিবেশের উপর প্রভাব)](https://offschool.site/subjects/physics/ch04/t05/)
  - [Topic: Relation between mass and energy (ভর ও শক্তির সম্পর্ক)](https://offschool.site/subjects/physics/ch04/t06/)
  - [Topic: Power (ক্ষমতা)](https://offschool.site/subjects/physics/ch04/t09/)
  - [Topic: Efficiency (কর্মদক্ষতা)](https://offschool.site/subjects/physics/ch04/t10/)
  - [Topic: Work and its calculation (কাজ এবং কাজের হিসাব)](https://offschool.site/subjects/physics/ch04/t07/)
  - [Topic: Development and the efficient use of energy (agriculture, education, health) (উন্নয়ন এবং শক্তির কার্যকর ব্যবহার (কৃষি, শিক্ষা, স্বাস্থ্য))](https://offschool.site/subjects/physics/ch04/t08/)
  - [Simulation: The gatekeeper's day of work (দারোয়ান চাচার সারা দিনের কাজ)](https://offschool.site/sim/ssc.physics.ch04.gatekeeper-work/): At the school gate, the gatekeeper has been sitting on his stool on guard since 8 in the morning, holding a 1.5 kg stick. Now and then he patrols beside the gate with the stick, at home time he pushes the heavy gate open, and at the end of the day he stretches and says, "Phew... I did a lot of work today." In the physics sense, how many joules of work did he do while sitting since the morning?
  - [Simulation: Kaptai Hydroelectric Plant: Energy Conversion and Loss Chain (কাপ্তাই জলবিদ্যুৎ কেন্দ্র: শক্তি রূপান্তর ও অপচয়ের ধাপ)](https://offschool.site/sim/ssc.physics.ch04.kaptai-energy-chain/): At the Kaptai hydroelectric plant, 100 MJ of lake water potential energy enters the turbine each second. With a 90% efficient turbine and 95% efficient generator, 85.5 MJ of electricity is generated. On an older grid line with 80% efficiency, 68.4 MJ reached homes. If the transmission lines operate at 92% efficiency, how much of the original 100 MJ reaches homes as electricity?
  - [Simulation: Porters and lifting power (কুলি ও মাল তোলার ক্ষমতা)](https://offschool.site/sim/ssc.physics.ch04.porter-lifting-power/): At Kamalapur station, Rahim lifts a 50 kg sack of rice onto a 2 m high luggage van in 4 s (his power is 245 W). Karim takes 8 s to lift the same sack to the same height. What will Karim's power be in W, and how will his work compare to Rahim's?
  - [Simulation: How much mass does Rooppur turn into energy each day? (রূপপুর দিনে কত ভর শক্তিতে বদলায়?)](https://offschool.site/sim/ssc.physics.ch04.rooppur-grams-a-day/): The two units of the Rooppur nuclear power plant in Pabna will supply about 2400 megawatts; for that, the reactors make about 173 gigawatt-hours of heat every day. Einstein's E = mc² says this energy comes from a little mass disappearing. How much mass is turned into energy each day?
  - [Simulation: Potential and kinetic energy on a slide (স্লিপারে বিভব ও গতিশক্তি)](https://offschool.site/sim/ssc.physics.ch04.slide-energy/): A 20 kg child slides down a smooth 5 m high park slide. With no friction, their speed at the bottom reaches 9.9 m/s. If a 40 kg teenager (twice the mass) slides down the exact same slide, what will their speed be at the bottom?
- [Chapter 5: States of Matter and Pressure (পদার্থের অবস্থা ও চাপ)](https://offschool.site/subjects/physics/ch06/)
  - [Topic: Kinetic molecular theory of matter (গতি পদার্থের আণবিক তত্ত্ব)](https://offschool.site/subjects/physics/ch06/t01/)
  - [Topic: Plasma state (প্লাজমা অবস্থা)](https://offschool.site/subjects/physics/ch06/t02/)
  - [Topic: Relation of pressure with force and area (driving a pin into a wall, pushing a pin through paper, and so on) (চাপের সাথে বল ও ক্ষেত্রফলের সম্পর্ক (দেয়ালে পিন ঢুকানো, কাগজে আলপিন ঢুকানো ইত্যাদি))](https://offschool.site/subjects/physics/ch06/t03/)
  - [Topic: Density (ঘনত্ব)](https://offschool.site/subjects/physics/ch06/t04/)
  - [Topic: Atmospheric pressure (বায়ুমণ্ডলের চাপ)](https://offschool.site/subjects/physics/ch06/t05/)
  - [Topic: Altitude and the change of atmospheric pressure (ভূপৃষ্ঠের উচ্চতা এবং বায়ুমণ্ডলের চাপের পরিবর্তন)](https://offschool.site/subjects/physics/ch06/t06/)
  - [Topic: Changes in atmospheric pressure and changes in the weather (বায়ুমণ্ডলীয় চাপের পরিবর্তন এবং আবহাওয়ার পরিবর্তন)](https://offschool.site/subjects/physics/ch06/t07/)
  - [Topic: Pressure at a point in a liquid at rest (স্থির তরলে মধ্যে কোন বিন্দুতে চাপ)](https://offschool.site/subjects/physics/ch06/t08/)
  - [Topic: Pressure of fluids and buoyancy (প্রবাহীর চাপ ও প্লবতা)](https://offschool.site/subjects/physics/ch06/t09/)
  - [Topic: Bodies float in water: Archimedes' principle (বস্তু পানিতে ভাসে: আর্কিমিডিসের নীতি)](https://offschool.site/subjects/physics/ch06/t10/)
  - [Topic: Pascal's law (প্যাসকেলের সূত্র)](https://offschool.site/subjects/physics/ch06/t11/)
  - [Topic: Stress and strain (পীড়ন ও বিকৃতি)](https://offschool.site/subjects/physics/ch06/t12/)
  - [Topic: Hooke's law (হুকের সূত্র)](https://offschool.site/subjects/physics/ch06/t13/)
  - [Simulation: How does a small push lift a whole car? (ছোট ধাক্কায় পুরো গাড়ি ওঠে কীভাবে?)](https://offschool.site/sim/ssc.physics.ch06.car-lift-pascal/): At a service centre in Gazipur, a mechanic pushes a small lever to raise a 1500 kg car on an oil-filled hydraulic lift. The small piston is 5 cm² and the large one 500 cm². If the large piston were twice as big (1000 cm²), what would the same push lift?
  - [Simulation: How much less does a thicker wire stretch? (মোটা তার কতটা কম লম্বা হয়?)](https://offschool.site/sim/ssc.physics.ch06.crane-cable-stretch/): The cables of the cranes at Chattogram port stretch slightly when they hold heavy containers. In class, a 2 m steel wire 1 mm across stretches 1.25 mm with 10 kg hanging from it. With the same load, how much would a wire 2 mm across stretch?
  - [Simulation: Same push: why does the pin enter the board but not hurt the thumb? (একই চাপে পিন বোর্ডে ঢোকে, আঙুলে লাগে না কেন?)](https://offschool.site/sim/ssc.physics.ch06.drawing-pin-pressure/): Mitu pins a holiday notice to the board, pressing the head of a drawing pin with her thumb with 20 newtons. The sharp point goes into the wooden board, yet her thumb doesn't hurt at all. The same force acts at both ends, so why the different result?
  - [Simulation: Spring balance at Karwan Bazar: Hooke's law (কারওয়ান বাজারের স্প্রিং নিক্তি: হুকের সূত্র)](https://offschool.site/sim/ssc.physics.ch06.fish-market-spring-balance/): At a Karwan Bazar fish stall, hanging a 1 kg hilsa on a spring balance stretches the spring by a certain amount until it comes to rest. Another customer asks for a fish of double the mass, 2 kg. When the 2 kg fish is hung on the balance, what will happen to the stretch of the spring?
  - [Simulation: Kaptai Dam and fluid pressure (কাপ্তাই বাঁধ ও তরলের চাপ)](https://offschool.site/sim/ssc.physics.ch06.kaptai-dam-pressure/): The wall of the Kaptai hydroelectric dam is built much thicker at the bottom than at the top. In fresh water (density 1000 kg/m³), the liquid pressure at a depth of 10 m is 98,000 Pa. If a sensor or diver descends to a depth of 20 m, how will the liquid pressure compare with that at 10 m?
  - [Simulation: Why does rice take longer to cook up a mountain? (পাহাড়ে ভাত সেদ্ধ হতে দেরি কেন?)](https://offschool.site/sim/ssc.physics.ch06.keokradong-rice-pot/): Camping on top of Keokradong in Bandarban (about 1000 metres), friends notice rice takes much longer to cook and the crisp packets in their bags have puffed up. At what temperature does water boil up there?
  - [Simulation: Barometer and liquid column height (ব্যারোমিটার ও তরল স্তম্ভের উচ্চতা)](https://offschool.site/sim/ssc.physics.ch06.mercury-barometer-column/): In Torricelli's barometer, standard atmospheric pressure (1.013 × 10⁵ Pa, or about 1 atm) balances a 76 cm (0.76 m) column of mercury (density 13,600 kg/m³). If a barometer is built using water (density 1000 kg/m³) instead of mercury, how tall a water column can atmospheric pressure hold up?
  - [Simulation: Molecular speed and temperature (পদার্থের অণুর গতি ও তাপমাত্রা)](https://offschool.site/sim/ssc.physics.ch06.molecule-speed-temperature/): In Dhaka air at 25 °C, nitrogen molecules continuously rush around at about 515 m/s. When water is cooled to solid ice at −10 °C, what happens to the motion of its molecules?
  - [Simulation: Why do objects float? (বস্তু কেন পানিতে ভাসে?)](https://offschool.site/sim/ssc.physics.ch06.what-floats/): At a boatyard, a 2 L block of mahogany wood (density 600 kg/m³) is placed in water, and 60% (0.60 fraction) of its volume stays submerged while floating. If the carpenter places a 4 times heavier, 8 L block of the exact same wood in water, what fraction of its volume will be submerged?
- [Chapter 6: Effect of Heat on Matter (বস্তুর ওপর তাপের প্রভাব)](https://offschool.site/subjects/physics/ch05/)
  - [Topic: Heat and temperature (তাপ ও তাপমাত্রা)](https://offschool.site/subjects/physics/ch05/t01/)
  - [Topic: Thermometric properties of matter (পদার্থের তাপমাত্রিক ধর্ম)](https://offschool.site/subjects/physics/ch05/t02/)
  - [Topic: Relation between the Fahrenheit, Celsius and Kelvin scales (ফারেনহাইট, সেলসিয়াস এবং কেলভিন স্কেলের মধ্যে সম্পর্ক)](https://offschool.site/subjects/physics/ch05/t03/)
  - [Topic: Rise in temperature of a body (বস্তুর তাপমাত্রা বৃদ্ধি)](https://offschool.site/subjects/physics/ch05/t04/)
  - [Topic: Thermal expansion of matter (পদার্থের তাপীয় প্রসারণ)](https://offschool.site/subjects/physics/ch05/t05/)
  - [Topic: Linear, superficial and cubical expansion of solids (কঠিন পদার্থের দৈর্ঘ্য, ক্ষেত্রফল এবং আয়তন সম্প্রসারণ)](https://offschool.site/subjects/physics/ch05/t06/)
  - [Topic: Apparent and real expansion of liquids (তরলের আপাত এবং প্রকৃত প্রসারণ)](https://offschool.site/subjects/physics/ch05/t07/)
  - [Topic: Expansion of gases (গ্যাসের প্রসারণ)](https://offschool.site/subjects/physics/ch05/t18/)
  - [Topic: Effect of heat on change of state (পদার্থের অবস্থার পরিবর্তনে তাপের প্রভাব)](https://offschool.site/subjects/physics/ch05/t08/)
  - [Topic: Melting, vaporisation and condensation (গলন, বাষ্পীভবন ও ঘনীভবন)](https://offschool.site/subjects/physics/ch05/t09/)
  - [Topic: Melting point and boiling point (গলনাংক ও স্ফুটনাংক)](https://offschool.site/subjects/physics/ch05/t10/)
  - [Topic: Effect of pressure on the melting point (গলনাংকের উপর চাপের প্রভাব)](https://offschool.site/subjects/physics/ch05/t11/)
  - [Topic: Boiling and evaporation (স্ফুটন ও বাষ্পায়ন)](https://offschool.site/subjects/physics/ch05/t12/)
  - [Topic: Latent heat of fusion and of vaporisation (গলন এবং বাষ্পীভবনের সুপ্ততাপ)](https://offschool.site/subjects/physics/ch05/t13/)
  - [Topic: Evaporation causes cooling (বাষ্পায়ন শীতলীকরণের কারণ)](https://offschool.site/subjects/physics/ch05/t14/)
  - [Topic: Effect of various factors on evaporation (বাষ্পায়নের উপর নিয়ামকের প্রভাব)](https://offschool.site/subjects/physics/ch05/t15/)
  - [Topic: Specific heat and heat capacity (আপেক্ষিক তাপ ও তাপ ধারণ ক্ষমতা)](https://offschool.site/subjects/physics/ch05/t16/)
  - [Topic: Fundamental principle of calorimetry (তাপ পরিমাপের মূলনীতি)](https://offschool.site/subjects/physics/ch05/t17/)
  - [Simulation: A blacksmith's hot iron in water: what's the final temperature? (কামারের লাল লোহা পানিতে: শেষ তাপমাত্রা কত?)](https://offschool.site/sim/ssc.physics.ch05.blacksmith-quench/): At the smithy a 1 kg iron blade at 200 °C is plunged into 1 kg of water at 25 °C. Shihab says the average is 112.5 °C, so the water must boil. If no heat escapes, at what temperature do the water and iron finally settle?
  - [Simulation: Why does a clay pot keep water cool in summer? (গরমে মাটির কলসির পানি ঠান্ডা থাকে কেন?)](https://offschool.site/sim/ssc.physics.ch05.clay-pot-cooling/): On a hot April afternoon water in a steel jug is warm, but water in a clay pot is pleasantly cool. Grandmother says clay is a cold material by nature. The outside of the pot feels damp. What really keeps the water cool, and will it work as well on a muggy monsoon day?
  - [Simulation: Why does the level drop first when you heat it? (গরম করলে তরলের তল প্রথমে নামে কেন?)](https://offschool.site/sim/ssc.physics.ch05.flask-level-dips/): Coloured alcohol fills a glass flask fitted with a narrow tube. As soon as it goes on the burner the level in the tube drops a little, then climbs. Riya says the liquid must have shrunk at first. Why does the level drop first, and is the rise you see in the tube the liquid's whole expansion?
  - [Simulation: Ice to steam: temperature and latent heat (বরফ থেকে বাষ্প: তাপমাত্রা ও সুপ্ততাপ)](https://offschool.site/sim/ssc.physics.ch05.ice-to-steam/): A pot containing 0.5 kg of ice at -10 °C is heated using a 1000 W electric heater. After 390 s, the ice melts and the water begins boiling at 100 °C. If the heater remains on at full power for several more minutes (e.g. up to 800 s), what will the temperature of the boiling water be?
  - [Simulation: Is 99 degrees nearly boiling? (৯৯ ডিগ্রি মানেই কি প্রায় ফুটন্ত?)](https://offschool.site/sim/ssc.physics.ch05.ninety-nine-degrees/): On a video call, Rafi's cousin in America says his body temperature is 99 degrees and he feels perfectly well. Rafi is amazed: water boils at 100 degrees, so how can anyone live at 99? Which scale is the cousin using, and what is that in Celsius and Kelvin?
  - [Simulation: Rail gap and thermal expansion (রেললাইনের ফাঁক ও তাপীয় প্রসারণ)](https://offschool.site/sim/ssc.physics.ch05.rail-gap-expansion/): Near Ishwardi, 12 m steel rails are laid in winter at 15 °C. In the blazing April sun, their temperature reaches 60 °C. How much expansion gap is needed between two consecutive rails?
  - [Simulation: Same heat: does water or copper get hotter? (একই তাপে পানি না তামা, কোনটি বেশি গরম হয়?)](https://offschool.site/sim/ssc.physics.ch05.water-vs-copper/): Two pans sit on the stove: one holds 1 kg of water, the other 1 kg of copper pieces, both at 25 °C. Each receives the same 42 kJ of heat. Lima says the same heat must make them equally hot. How much does each one's temperature rise?
  - [Simulation: A loaded wire sinks through ice, yet the ice stays whole: why? (ভার ঝোলানো তার বরফ কেটে নামে, অথচ বরফ ভাঙে না কেন?)](https://offschool.site/sim/ssc.physics.ch05.wire-through-ice/): A thin wire is hung over a block of factory ice with 10 kg tied at each end. After a while the wire has sunk right through the ice and dropped out of the bottom, yet the block is still in one piece. Tania says friction heated the wire and it melted the ice. What really happens?
- [Chapter 7: Waves and Sound (তরঙ্গ ও শব্দ)](https://offschool.site/subjects/physics/ch07/)
  - [Topic: Simple harmonic motion (সরল স্পন্দন গতি)](https://offschool.site/subjects/physics/ch07/t12/)
  - [Topic: Types and characteristics of waves (তরঙ্গের প্রকারভেদ এবং বৈশিষ্ট্য)](https://offschool.site/subjects/physics/ch07/t01/)
  - [Topic: Quantities of a wave and their mathematical relations (তরঙ্গ সংশ্লিষ্ট রাশি এবং গাণিতিক সম্পর্ক)](https://offschool.site/subjects/physics/ch07/t02/)
  - [Topic: Sound waves (শব্দ তরঙ্গ)](https://offschool.site/subjects/physics/ch07/t03/)
  - [Topic: Production of an echo (প্রতিধ্বনি সৃষ্টি)](https://offschool.site/subjects/physics/ch07/t04/)
  - [Topic: Uses of echoes (প্রতিধ্বনির ব্যবহার)](https://offschool.site/subjects/physics/ch07/t05/)
  - [Topic: Mathematical relation between the velocity, frequency and wavelength of sound (শব্দের বেগ, কম্পাংক এবং তরঙ্গদৈর্ঘ্যের গাণিতিক সম্পর্ক)](https://offschool.site/subjects/physics/ch07/t06/)
  - [Topic: Variation of the velocity of sound (medium, temperature) (শব্দের বেগের পরিবর্তন (মাধ্যম, তাপমাত্রা))](https://offschool.site/subjects/physics/ch07/t07/)
  - [Topic: Audible range and uses of sound (শ্রাব্যতার সীমা ও শব্দের ব্যবহার)](https://offschool.site/subjects/physics/ch07/t08/)
  - [Topic: Pitch and intensity (পীচ ও তীব্রতা)](https://offschool.site/subjects/physics/ch07/t09/)
  - [Topic: Musical sound (সুরযুক্ত শব্দ)](https://offschool.site/subjects/physics/ch07/t13/)
  - [Topic: Sound pollution (শব্দ দূষণ)](https://offschool.site/subjects/physics/ch07/t10/)
  - [Topic: Ways of prevention (প্রতিরেধের কৌশল)](https://offschool.site/subjects/physics/ch07/t11/)
  - [Simulation: Echo in a well and distance (কূপে প্রতিধ্বনি ও দূরত্ব)](https://offschool.site/sim/ssc.physics.ch07.echo-in-a-well/): A student shouts down into a deep, dry well. At an air temperature of 30 °C, the speed of sound is 350 m/s. When the bottom is at a distance of 35 m, the echo returns in 0.20 s. If the distance to the bottom doubles to 70 m, after how much time will the echo be heard?
  - [Simulation: Flute to dog whistle: frequency and wavelength (বাঁশির সুর থেকে কুকুরের বাঁশি: কম্পাঙ্ক ও তরঙ্গদৈর্ঘ্য)](https://offschool.site/sim/ssc.physics.ch07.flute-to-dog-whistle/): At a village fair, a flute plays a note at 440 Hz. A dog whistle sounds at 25,000 Hz (25 kHz), and elephants rumble at 15 Hz. At 30 °C, the speed of sound in air is 350 m/s. The dog whistle has a much higher frequency than the flute. What will happen to the speed and wavelength of this higher frequency sound in the air?
  - [Simulation: Is a horn still harmful 10 metres away? (হর্ন থেকে ১০ মিটার দূরেও কি ক্ষতি?)](https://offschool.site/sim/ssc.physics.ch07.hydraulic-horn-noise/): On a Dhaka road, a bus's hydraulic horn measures about 110 decibels at 1 metre. Rima, a schoolgirl on the pavement, is 10 metres from the horn. Sound gets quieter with distance. What is the sound level where Rima stands?
  - [Simulation: Sound on the rails: medium and sound speed (রেললাইনে শব্দ: মাধ্যম ও শব্দের বেগ)](https://offschool.site/sim/ssc.physics.ch07.rail-knock-sound-speed/): Standing near a level crossing in Tongi, Rafi notices that the knock of a hammer on the rail 255 m away arrives through the steel track long before it travels through the air. What is the order of sound speeds across steel (solid), water (liquid), and air (gas)?
  - [Simulation: Wave frequency and wavelength on a rope (দড়িতে তরঙ্গের কম্পাঙ্ক ও তরঙ্গদৈর্ঘ্য)](https://offschool.site/sim/ssc.physics.ch07.rope-wave-frequency/): One end of a long rope tied to a mango tree is shaken at a steady rate to produce waves that travel at 4 m/s. At first, shaking 2 times a second (frequency 2 Hz) produces waves with a wavelength of 2 m. If the shaking frequency is doubled to 4 Hz, what will the wavelength become?
  - [Simulation: What changes when sound goes under water? (পানির নিচে শব্দের কী বদলায়?)](https://offschool.site/sim/ssc.physics.ch07.sound-under-water/): Diving in a pond, Tuhin hears a friend on the bank blowing a 1000 hertz whistle. Sound travels 343 metres a second in air and about 1500 in water. Entering the water, what happens to the sound's frequency, speed and wavelength?
  - [Simulation: Ultrasound Echo and Organ Depth (আল্ট্রাসনোগ্রাফিতে প্রতিধ্বনি ও অঙ্গের গভীরতা)](https://offschool.site/sim/ssc.physics.ch07.ultrasound-echo/): An abdominal ultrasound scan is being performed on a patient. In soft body tissue, ultrasound travels at 1540 m/s. An organ at a depth of 0.077 m (7.7 cm) returns an echo in 1×10⁻⁴ s. If the doctor examines a deeper organ at a depth of 0.154 m (15.4 cm), what will the echo return time be?
  - [Simulation: The wall clock's pendulum: simple harmonic motion (দেয়ালঘড়ির দোলক: সরল ছন্দিত গতি)](https://offschool.site/sim/ssc.physics.ch07.wall-clock-pendulum/): The classroom wall clock's pendulum is 1 m long and swings with an amplitude of about 5 degrees. The clock runs a little slow, so Roni says swinging the pendulum harder, at 10 degrees, will make each swing finish sooner. What happens to the period when the amplitude is doubled?
- [Chapter 8: Reflection of Light (আলোর প্রতিফলন)](https://offschool.site/subjects/physics/ch08/)
  - [Topic: Nature of light (আলোর প্রকৃতি)](https://offschool.site/subjects/physics/ch08/t01/)
  - [Topic: Laws of reflection of light (আলোর প্রতিফলনের সূত্র)](https://offschool.site/subjects/physics/ch08/t02/)
  - [Topic: Mirrors: plane and spherical (concave, convex) (দর্পণ: সমতল ও গোলীয় (অবতল, উত্তল))](https://offschool.site/subjects/physics/ch08/t03/)
  - [Topic: Images: real and virtual (প্রতিবিম্ব: বাস্তব ও অবাস্তব)](https://offschool.site/subjects/physics/ch08/t04/)
  - [Topic: Image formed in a mirror (দর্পণে আলোর প্রতিবিম্ব)](https://offschool.site/subjects/physics/ch08/t05/)
  - [Topic: Some common cases of image formation in plane and spherical mirrors (সমতল ও গোলীয় দর্পণে প্রতিবিম্ব সৃষ্টির কিছু সাধারণ ঘটনা)](https://offschool.site/subjects/physics/ch08/t06/)
  - [Topic: Uses of mirrors (দর্পণের ব্যবহার)](https://offschool.site/subjects/physics/ch08/t07/)
  - [Topic: Magnification (বিবর্ধন)](https://offschool.site/subjects/physics/ch08/t08/)
  - [Simulation: How many images in the barber's two mirrors? (সেলুনের দুই আয়নায় কয়টি প্রতিবিম্ব?)](https://offschool.site/sim/ssc.physics.ch08.barber-shop-mirrors/): In a barber's shop two mirrors stand at an angle, and Sakib, sitting between them, sees many images of himself. The barber says the angle between the mirrors is 60 degrees. How many images of himself will Sakib see?
  - [Simulation: Choosing the right mirror (কাজের প্রয়োজনে সঠিক দর্পণ নির্বাচন)](https://offschool.site/sim/ssc.physics.ch08.choose-the-mirror/): A salon shaving mirror, a rickshaw side mirror, and a round mirror at a blind turn on a Bandarban hill road: different tasks need different mirrors. A round mirror (focal length 20 cm) is installed at a blind hill bend. Drivers must see an oncoming car 50 cm away upright and smaller in size to fit the whole road into view. Which mirror should be chosen?
  - [Simulation: Image position and nature in a concave mirror (অবতল দর্পণে প্রতিবিম্বের অবস্থান ও প্রকৃতি)](https://offschool.site/sim/ssc.physics.ch08.concave-mirror-image/): Standing 30 cm in front of a concave makeup mirror of focal length 10 cm, Anika notices that her reflection is inverted and diminished. At what distance from the mirror must she place her face to see an upright and magnified image?
- [Chapter 9: Refraction of Light (আলোর প্রতিসরণ)](https://offschool.site/subjects/physics/ch09/)
  - [Topic: Laws of refraction of light (আলোর প্রতিসরণের সূত্র)](https://offschool.site/subjects/physics/ch09/t01/)
  - [Topic: Refractive index (প্রতিসরাঙ্ক)](https://offschool.site/subjects/physics/ch09/t02/)
  - [Topic: Critical angle and total internal reflection (ক্রান্তি কোণ ও পূর্ণ অভ্যন্তরীণ প্রতিফলন)](https://offschool.site/subjects/physics/ch09/t03/)
  - [Topic: Rainbow and mirage (রংধনু ও মরীচিকা)](https://offschool.site/subjects/physics/ch09/t16/)
  - [Topic: Optical fibre (অপটিক্যাল ফাইবার)](https://offschool.site/subjects/physics/ch09/t04/)
  - [Topic: Its use in telecommunication and health care (টেলিকমিউনিকেশন এবং স্বাস্থ্য ক্ষেত্রে এর ব্যবহার)](https://offschool.site/subjects/physics/ch09/t05/)
  - [Topic: Uses of refraction of light (আলোর প্রতিসরণের ব্যবহার)](https://offschool.site/subjects/physics/ch09/t06/)
  - [Topic: Prism, periscope and binocular (প্রিজম, পেরিস্কোপ ও বাইনোকুলার)](https://offschool.site/subjects/physics/ch09/t17/)
  - [Topic: Lenses and their types (লেন্স এবং লেন্সের প্রকারভেদ)](https://offschool.site/subjects/physics/ch09/t07/)
  - [Topic: Quantities related to a lens (লেন্স সংক্রান্ত রাশি)](https://offschool.site/subjects/physics/ch09/t08/)
  - [Topic: Formation of an image by a lens (লেন্সে প্রতিবিম্ব সৃষ্টি)](https://offschool.site/subjects/physics/ch09/t09/)
  - [Topic: Power of a lens (লেন্সের ক্ষমতা)](https://offschool.site/subjects/physics/ch09/t10/)
  - [Simulation: Lateral shift through aquarium glass (অ্যাকুয়ারিয়ামের কাচে আলোর পার্শ্ব সরণ)](https://offschool.site/sim/ssc.physics.ch09.aquarium-glass-shift/): Looking at colourful fish through the thick glass wall of an aquarium shop in Katabon, Dhaka, the fish appear shifted sideways from their actual position. Suppose the parallel glass wall has a thickness of 5 cm and a refractive index of 1.50 (surrounding air index is 1.00). A ray of light from air strikes the glass at an angle of incidence of 30°. After refracting through the glass and emerging back into the air on the other side, what will be the direction of the light ray?
  - [Simulation: The bent straw in water: Refraction of light (পানিতে স্ট্র বাঁকা দেখার রহস্য: আলোর প্রতিসরণ)](https://offschool.site/sim/ssc.physics.ch09.bent-straw-refraction/): When a straight straw is immersed in a glass of water, it looks bent or broken at the surface when viewed from above. When light enters obliquely from air (n₁ = 1.00) into water (n₂ = 1.33), which way does the ray bend? And what happens if the ray enters perpendicularly along the normal (incident angle 0°)?
  - [Simulation: Critical angle and total internal reflection (ক্রান্তি কোণ ও পূর্ণ অভ্যন্তরীণ প্রতিফলন)](https://offschool.site/sim/ssc.physics.ch09.critical-angle/): An optical fibre broadband internet cable has a glass core with refractive index n₁ = 1.5 surrounded by air with n₂ = 1.0. The critical angle for this boundary is about 42° (41.8°). Initially, light enters at an angle of incidence of 30° and refracts out into the air. If the engineer increases the angle of incidence beyond the critical angle to 50°, what will happen to the light ray?
  - [Simulation: Grandfather's magnifying glass: Images in a convex lens (দাদুর আতশ কাচ: উত্তল লেন্সে প্রতিবিম্ব)](https://offschool.site/sim/ssc.physics.ch09.grandfather-magnifier/): Grandfather is reading the morning newspaper using a magnifying glass (convex lens) with a focal length of 10 cm. Holding it 30 cm away makes the letters appear inverted and small. At what distance from the paper must he place the magnifying glass to see upright and enlarged letters?
  - [Simulation: Power of a spectacle lens (চশমার লেন্সের ক্ষমতা)](https://offschool.site/sim/ssc.physics.ch09.optician-lens-power/): At an optician shop in Nilkhet, Nabila's prescription reads -2.0 D and her friend's reads +2.5 D. What type of lens is needed for her friend's glasses, and what must its focal length be?
  - [Simulation: A rainbow from a prism: which colour bends most (প্রিজমে রংধনু: কোন রঙ বেশি বাঁকে)](https://offschool.site/sim/ssc.physics.ch09.rainbow-prism/): In the sunlight at the window Mitu holds a glass prism, and a band of colours from red to violet appears on the wall. Glass has a refractive index of about 1.51 for red light and about 1.53 for violet. Which colour is bent the most by the prism?
- [Chapter 10: Static Electricity (স্থির বিদ্যুৎ)](https://offschool.site/subjects/physics/ch10/)
  - [Topic: Production of static electricity (স্থির তড়িৎ সৃষ্টি)](https://offschool.site/subjects/physics/ch10/t01/)
  - [Topic: Detecting charge: use of the electroscope (চার্জ শনাক্তকরণ: তড়িৎবীক্ষণ যন্ত্রের ব্যবহার)](https://offschool.site/subjects/physics/ch10/t02/)
  - [Topic: Measuring the electric force: Coulomb's law (তড়িৎ বলের পরিমাপ-কুলম্বের সূত্র)](https://offschool.site/subjects/physics/ch10/t03/)
  - [Topic: Intensity and direction of an electric field through electric lines of force (তড়িৎ বলরেখার মাধ্যমে তড়িৎ ক্ষেত্রের প্রাবল্য ও এর দিক ব্যাখ্যা)](https://offschool.site/subjects/physics/ch10/t04/)
  - [Topic: Electric potential (তড়িৎ বিভব)](https://offschool.site/subjects/physics/ch10/t05/)
  - [Topic: Storing electrical energy: the capacitor (তড়িৎ শক্তি সংরক্ষণ: ধারক)](https://offschool.site/subjects/physics/ch10/t06/)
  - [Topic: Uses of static electricity (স্থির তড়িতের ব্যবহার)](https://offschool.site/subjects/physics/ch10/t07/)
  - [Topic: Dangers of static electricity and safety measures (স্থির তড়িতের ঝুঁকি এবং নিরাপত্তা কৌশল)](https://offschool.site/subjects/physics/ch10/t08/)
  - [Simulation: How much more does a capacitor hold with its plates closer? (পাত কাছে আনলে ধারক কতটা বেশি ধরে?)](https://offschool.site/sim/ssc.physics.ch10.camera-flash-capacitor/): A camera flash stores electrical energy in a capacitor so it can fire in an instant. Nafis makes a capacitor from two metal plates with 1 mm of air between them. If he brings the plates closer, to a 0.5 mm gap, what happens to the capacitance?
  - [Simulation: Attraction between charges and Coulomb's law (স্থির চার্জের আকর্ষণ ও কুলম্বের সূত্র)](https://offschool.site/sim/ssc.physics.ch10.charges-attract-repel/): A plastic comb rubbed on dry hair acquires a charge of -2 µC and attracts a +2 µC charged piece of paper. At a separation of 0.3 m, the attractive force is 0.4 N. If the comb is brought closer so the separation is halved to 0.15 m, what will the attractive force become?
  - [Simulation: Electric potential between opposite charges (বিপরীত আধানের মধ্যবর্তী তড়িৎ বিভব)](https://offschool.site/sim/ssc.physics.ch10.dipole-potential/): In a physics lab, two small metal spheres carrying charges of +4 µC and −4 µC are fixed 0.4 m apart in air. What is the electric potential at the midpoint between the two charges (0.2 m from each charge)? (Coulomb's constant k = 9 × 10⁹ N m² C⁻²)
  - [Simulation: Why do the leaves fall when the rod goes? (দণ্ড সরালে পাতা কেন বুজে যায়?)](https://offschool.site/sim/ssc.physics.ch10.electroscope-leaves/): In the physics lab, the teacher brings an ebonite rod rubbed with fur near the cap of a gold-leaf electroscope, without touching it. The two leaves spread apart. If the rod is now taken away, what happens to the leaves?
  - [Simulation: Electric field and neutral point (তড়িৎ ক্ষেত্র ও নিরপেক্ষ বিন্দু)](https://offschool.site/sim/ssc.physics.ch10.neutral-point-field/): A charged comb brought close makes a hanging thread lean towards it: every charged body sets up an electric field around itself. Two like positive charges sit on a line 0.3 m apart: q1 = +2 µC and q2 = +2 µC. If a test charge is placed exactly at their midpoint (x = 0, y = 0), what will the electric field strength be?
- [Chapter 11: Current Electricity (চল বিদ্যুৎ)](https://offschool.site/subjects/physics/ch11/)
  - [Topic: Production of current electricity from static electricity (স্থির তড়িৎ হতে চল তড়িৎ সৃষ্টি)](https://offschool.site/subjects/physics/ch11/t01/)
  - [Topic: Direction of electric current and direction of electron flow (তড়িৎ প্রবাহের দিক এবং ইলেকট্রন প্রবাহের দিক)](https://offschool.site/subjects/physics/ch11/t02/)
  - [Topic: Electrical symbols: switch (one-way, two-way), cell, battery, fixed resistor, variable resistor, source (AC and DC), fuse, load, ammeter, voltmeter, galvanometer, earth connection, crossing wires, joined wires, capacitor (তড়িৎ প্রতীক: সুইচ (একমুখী, দ্বিমুখী), কোষ, ব্যাটারি, স্থির রোধ, পরিবর্তনশীল রোধ, তড়িৎ উৎস (এসি ও ডিসি), ফিউজ, লোড, অ্যামিটার, ভোল্টমিটার, গ্যালভানোমিটার, ভূ-সংযোগ, আড়াআড়ি তার, প্যাঁচানো তার, ধারক)](https://offschool.site/subjects/physics/ch11/t03/)
  - [Topic: Conductors, insulators and semiconductors (পরিবাহী, অপরিবাহী এবং অর্ধপরিবাহী)](https://offschool.site/subjects/physics/ch11/t04/)
  - [Topic: Relation between potential difference and electric current: Ohm's law (বিভব পার্থক্য এবং তড়িৎ প্রবাহের মধ্যে সম্পর্ক-ওহমের সূত্র)](https://offschool.site/subjects/physics/ch11/t05/)
  - [Topic: Fixed and variable resistors (স্থির এবং পরিবর্তনশীল রোধ)](https://offschool.site/subjects/physics/ch11/t06/)
  - [Topic: Electromotive force and potential difference (তড়িৎচালক বল এবং বিভব পার্থক্য)](https://offschool.site/subjects/physics/ch11/t07/)
  - [Topic: Dependence of resistance (রোধের নির্ভশীলতা)](https://offschool.site/subjects/physics/ch11/t08/)
  - [Topic: Resistivity and conductivity (রোধকতা ও পরিবাহিতা)](https://offschool.site/subjects/physics/ch11/t09/)
  - [Topic: Making and using series and parallel circuits (শ্রেণি এবং সমান্তরাল বর্তনী তৈরি ও ব্যবহার)](https://offschool.site/subjects/physics/ch11/t10/)
  - [Topic: Equivalent resistance and its use in circuits (তুল্যরোধ এবং বর্তনীতে তুল্যরোধের ব্যবহার)](https://offschool.site/subjects/physics/ch11/t11/)
  - [Topic: Calculation of electric power (তড়িৎ ক্ষমতার হিসাব)](https://offschool.site/subjects/physics/ch11/t12/)
  - [Topic: System loss and load shedding (তড়িতের সিস্টেম লস এবং লোড শেডিং)](https://offschool.site/subjects/physics/ch11/t13/)
  - [Topic: Safe and efficient use of electricity (তড়িতের নিরাপদ ও কার্যকর ব্যবহার)](https://offschool.site/subjects/physics/ch11/t14/)
  - [Topic: Designing an electric circuit suitable for a house and demonstrating its use (বাসা বাড়ির উপযোগী তড়িৎ বর্তনীর নকশা প্রণয়ন এবং ব্যবহার প্রদর্শন)](https://offschool.site/subjects/physics/ch11/t15/)
  - [Simulation: Cell EMF and Terminal Potential Difference (কোষের তড়িচ্চালক বল ও প্রান্তীয় বিভব পার্থক্য)](https://offschool.site/sim/ssc.physics.ch11.cell-internal-resistance/): A battery with an emf (E) of 6 V and an internal resistance (r) of 1 Ω is connected to a switch and a lamp. A voltmeter is connected across the battery terminals. With the switch on (closed), a current of 1.2 A flows and the voltmeter reads a terminal pd of 4.8 V. If the switch is now turned off (opened), what will the voltmeter read?
  - [Simulation: Testing Conductors and Insulators (পরিবাহী ও অপরিবাহী পদার্থ পরীক্ষা)](https://offschool.site/sim/ssc.physics.ch11.conductor-insulator-tester/): An electrician is testing the electrical conductivity of materials using a tester circuit. The circuit has a 6 V battery, a 6 V 6 W torch bulb, and an open gap between two test probes. Three materials are tested in the gap: copper wire, pencil lead (graphite), and a plastic ruler. Which of these materials will make the bulb glow dimly: neither completely dark nor shining at full brightness?
  - [Simulation: Why copper for wiring and nichrome for heaters? (বাড়ির তারে তামা, হিটারে নাইক্রোম কেন?)](https://offschool.site/sim/ssc.physics.ch11.copper-or-nichrome-wire/): House wiring is copper, while the coil of a water heater is nichrome. With 10 amperes through wires of the same size (10 m, 1.5 mm²), how much heat does the nichrome wire make compared with the copper?
  - [Simulation: Does doubling regulator resistance halve the current? (রেগুলেটরের রোধ দ্বিগুণ করলে প্রবাহ কি অর্ধেক হয়?)](https://offschool.site/sim/ssc.physics.ch11.fan-regulator-rheostat/): Old ceiling fan regulators contain coils of resistance wire. Turning the knob changes the length of wire connected in the circuit. On the board below, a 12 V battery is connected in series with a regulator (rheostat), a 12 V 36 W lamp, and an ammeter, with a voltmeter across the lamp. With the regulator resistance set at 2 Ω, the ammeter shows a current of 2 A. If the knob is turned to double the wire length in the circuit, making its resistance 4 Ω, what current will the ammeter show?
  - [Simulation: Why does one dead bulb put out the whole string? (মরিচবাতির একটি বাল্ব কাটলে সব নেভে কেন?)](https://offschool.site/sim/ssc.physics.ch11.festival-lights/): At a wedding, when one bulb in a string of fairy lights dies, the whole string goes dark. On the board below, two 6 V 3 W bulbs are connected in series to a 6 V battery, and both glow rather dimly. If the filament of the bulb in box 2 breaks, what happens to the bulb in box 1? And how would you connect them so that both glow at full brightness?
  - [Simulation: How long does a capacitor light a bulb? (ধারক দিয়ে বাতি কতক্ষণ জ্বলে?)](https://offschool.site/sim/ssc.physics.ch11.flash-from-a-capacitor/): Rubbing a comb through hair builds up static charge. A 1000 µF capacitor is charged to 6 V and connected to a torch bulb. A battery keeps the bulb lit for hours. How long will the capacitor light it?
  - [Simulation: Is Current Used Up in a Series Circuit? (শ্রেণিবর্তনীতে তড়িৎ প্রবাহ কি কমে যায়?)](https://offschool.site/sim/ssc.physics.ch11.is-current-used-up/): Two bulbs of 3 Ω and 3 Ω are connected in series with a 12 V battery. A total current of 2 A flows through the circuit, with 2 A passing through the first bulb. If the first bulb is replaced with a 9 Ω bulb, how many amperes of current will flow through the second bulb (3 Ω)?
  - [Simulation: The Monthly Electricity Bill: How Many Units Were Used? (মাস শেষে বিদ্যুৎ বিল: কত ইউনিট খরচ হলো?)](https://offschool.site/sim/ssc.physics.ch11.monthly-electricity-units/): A 100 W bulb is on for 5 hours every day. How many units of electricity does it use in 30 days?
  - [Simulation: Why does overloading a power strip blow the fuse? (মাল্টিপ্লাগে অতিরিক্ত লোড দিলে ফিউজ কাটে কেন?)](https://offschool.site/sim/ssc.physics.ch11.overloaded-socket-fuse/): A multi-plug with a 5 A fuse is connected to a 220 V mains line. Two 440 W heaters (each drawing 2 A) are running in parallel in sockets 1 and 2. What will happen if a third identical 440 W heater (2 A) is plugged into socket 3?
  - [Simulation: Electric Power and Line Loss (তড়িৎ ক্ষমতা ও লাইনে অপচয়)](https://offschool.site/sim/ssc.physics.ch11.power-and-electric-bill/): A transmission line of resistance r = 6 Ω is connected in series with an 18 Ω lamp. The power supply voltage is set to v = 24 V. A current of 1.0 A flows, delivering 18 W to the lamp while wasting 6 W in the line (25% of total power). When delivering a fixed power to the load, which case causes greater heat loss (system loss) in the line?
  - [Simulation: Three Resistors in Parallel: What Is the Equivalent Resistance? (তিনটি রোধ সমান্তরালে: তুল্যরোধ কত?)](https://offschool.site/sim/ssc.physics.ch11.three-resistors-parallel/): Three resistors of 2 Ω, 3 Ω and 6 Ω are connected in parallel across a 6 V battery. What is their equivalent resistance, and how much current does the battery supply?
  - [Simulation: Torch Circuit and Switch Operation (টর্চের বর্তনী ও সুইচের কাজ)](https://offschool.site/sim/ssc.physics.ch11.torch-circuit-switch/): A torch has a 1.5 V cell, a one-way switch, a 3 Ω bulb, and an ammeter connected in a series loop. With the switch on (closed), a current of 0.5 A flows and the bulb glows dimly. If the switch is now turned off (opened), what current in amperes will the ammeter show?
- [Chapter 12: Magnetic Effects of Current (বিদ্যুতের চৌম্বক ক্রিয়া)](https://offschool.site/subjects/physics/ch12/)
  - [Topic: Magnet (চুম্বক)](https://offschool.site/subjects/physics/ch12/t07/)
  - [Topic: Magnetic effect of the current in a conductor (পরিবাহিতে তড়িৎ প্রবাহের কারণে চৌম্বক প্রভাব)](https://offschool.site/subjects/physics/ch12/t01/)
  - [Topic: Solenoid (সলিনয়েড)](https://offschool.site/subjects/physics/ch12/t08/)
  - [Topic: Electromagnet (তড়িৎচুম্বক)](https://offschool.site/subjects/physics/ch12/t09/)
  - [Topic: Effect of a magnet on a current-carrying wire (তড়িৎবাহী তারের ওপর চুম্বকের প্রভাব)](https://offschool.site/subjects/physics/ch12/t10/)
  - [Topic: Electromagnetic induction (তড়িৎ চুম্বকীয় আবেশ)](https://offschool.site/subjects/physics/ch12/t02/)
  - [Topic: Induced current and induced potential difference (আবিষ্ট তড়িৎ প্রবাহ এবং আবিষ্ট বিভব পার্থক্য)](https://offschool.site/subjects/physics/ch12/t03/)
  - [Topic: Principle and working of the motor and the generator (মটর এবং জেনারেটরের মূলনীতি ও কার্যক্রম)](https://offschool.site/subjects/physics/ch12/t04/)
  - [Topic: Principle of the transformer (ট্রান্সফরমারের মূলনীতি)](https://offschool.site/subjects/physics/ch12/t05/)
  - [Topic: Working of step-up and step-down transformers (স্টেপ আপ ও স্টেপ ডাউন ট্রান্সফরমার কার্যক্রম)](https://offschool.site/subjects/physics/ch12/t06/)
  - [Simulation: Bicycle dynamo: induced voltage (সাইকেলের ডায়নামো ও আবিষ্ট তড়িৎ বিভব)](https://offschool.site/sim/ssc.physics.ch12.bicycle-dynamo-emf/): A bottle dynamo on a bicycle wheel powers a headlamp while cycling home on a village road at night. The dynamo coil has an area of 20 cm², a magnetic field of 0.50 T, and 100 turns. When spinning at 600 rpm, its peak induced emf is about 6.3 V (frequency 10 Hz). If the cyclist pedals faster and doubles the rotation speed to 1200 rpm, what will the peak induced voltage become?
  - [Simulation: Phone charger transformer: voltage step-down (মোবাইল চার্জারে ট্রান্সফরমার ও ভোল্টেজ রূপান্তর)](https://offschool.site/sim/ssc.physics.ch12.phone-charger-transformer/): Household mains supply 220 V AC, but a mobile phone needs only 5 V to charge. A charger contains a step-down transformer with 2200 turns in the primary coil and 50 turns in the secondary coil. If the secondary coil turns are doubled to 100, what will the output voltage (secondary voltage) become?
  - [Simulation: Ship-breaking crane electromagnet (জাহাজভাঙা কারখানায় ক্রেনের তড়িৎচুম্বক)](https://offschool.site/sim/ssc.physics.ch12.scrapyard-electromagnet/): At the Sitakunda ship-breaking yard, a crane electromagnet lifts heavy steel plates. The 0.5 m coil has 500 turns around a soft-iron core. Passing 4 A of current produces a strong magnetic field of about 1000 mT. If the iron core is pulled out leaving only air inside, what happens to the magnetic field?
- [Chapter 13: Radioactivity and Electronics (তেজস্ক্রিয়তা ও ইলেকট্রনিকস)](https://offschool.site/subjects/physics/ch13/)
  - [Topic: Radioactivity (তেজস্ক্রিয়তা)](https://offschool.site/subjects/physics/ch13/t01/)
  - [Topic: Alpha, beta and gamma rays (আলফা, বিটা ও গামা রশ্মি)](https://offschool.site/subjects/physics/ch13/t02/)
  - [Topic: Half-life (অর্ধায়ু)](https://offschool.site/subjects/physics/ch13/t09/)
  - [Topic: Uses of radioactivity and cautions (তেজস্ক্রিয়তার ব্যবহার ও সতর্কতা)](https://offschool.site/subjects/physics/ch13/t10/)
  - [Topic: Development of electronics (ইলেকট্রনিকসের ক্রমবিকাশ)](https://offschool.site/subjects/physics/ch13/t03/)
  - [Topic: Analogue and digital electronics (অ্যানালগ ও ডিজিটাল ইলেকট্রনিকস)](https://offschool.site/subjects/physics/ch13/t04/)
  - [Topic: Semiconductors and integrated circuits (অর্ধপরিবাহী ও সমন্বিত বর্তনী)](https://offschool.site/subjects/physics/ch13/t05/)
  - [Simulation: Will the lamp light with the diode turned round? (ডায়োড উল্টে দিলে বাতি জ্বলবে?)](https://offschool.site/sim/ssc.physics.ch13.diode-one-way-street/): Inside a phone charger are little black diodes. Joy connects a battery, a diode and a lamp, and the lamp lights. Now he turns the diode round. What happens to the lamp?
  - [Simulation: Radioactive decay and half-life (তেজস্ক্রিয় ক্ষয় ও অর্ধায়ু)](https://offschool.site/sim/ssc.physics.ch13.hospital-isotope-decay/): At a nuclear medicine centre in Dhaka, Technetium-99m is administered to a patient for imaging. This isotope has a half-life of 6 hours, so it clears from the body within a couple of days. Initially, 1600 radioactive nuclei are present. What fraction remains undecayed after 24 hours?
  - [Simulation: Which wall stops gamma rays? (গামা রশ্মি আটকাতে কোন দেয়াল?)](https://offschool.site/sim/ssc.physics.ch13.hospital-radiation-shield/): A cancer hospital in Dhaka treats patients with gamma rays from cobalt-60. A builder asks: if the room is lined with paper, aluminium sheet or thick lead, which one lets no radiation out at all?
  - [Simulation: Logic gates and doorbell circuit (লজিক গেট ও কলিংবেল বর্তনী)](https://offschool.site/sim/ssc.physics.ch13.logic-gate-doorbell/): A house doorbell or alarm circuit has two switches, A and B. With an OR gate, turning either switch ON (1) rings the bell, while with an AND gate, both switches must be ON (1) for the bell to ring. Now switch A is ON (1) and switch B is OFF (0). If a NAND gate is used in the circuit, what will the output Y be (will the bell ring)?

## Chemistry (রসায়ন)

States of matter, atomic structure, the periodic table, bonding, the mole, reactions, acids and bases, and minerals, the world of atoms in front of you.

- [SSC Chemistry](https://offschool.site/subjects/chemistry/): পদার্থের অবস্থা, পরমাণুর গঠন, পর্যায় সারণি, রাসায়নিক বন্ধন, মোল, বিক্রিয়া, এসিড-ক্ষার আর খনিজ সম্পদ, অণু-পরমাণুর জগৎ চোখের সামনে।
- [SSC Chemistry formula sheet](https://offschool.site/subjects/chemistry/formulas/): every formula, chapter by chapter, each with its simulation.
- [Chapter 1: Concepts of Chemistry (রসায়নের ধারণা)](https://offschool.site/subjects/chemistry/ch01/)
  - [Topic: Introduction to chemistry (রসায়ন পরিচিতি)](https://offschool.site/subjects/chemistry/ch01/t01/)
  - [Topic: Identifying the fields of chemistry (রসায়নের ক্ষেত্রসমূহ চিহ্নিতকরণ)](https://offschool.site/subjects/chemistry/ch01/t02/)
  - [Topic: Scope of chemistry: medicine, daily life, construction, industry, food preservation and agriculture (রসায়নের পরিধি: চিকিৎসা, দৈনন্দিন জীবন, নির্মাণ, শিল্প, খাদ্য সংরক্ষণ ও কৃষি)](https://offschool.site/subjects/chemistry/ch01/t03/)
  - [Topic: Relation of chemistry with other branches of science (বিজ্ঞানের অন্যান্য শাখার সাথে রসায়নের সম্পর্ক)](https://offschool.site/subjects/chemistry/ch01/t04/)
  - [Topic: Making and presenting a chart of chemistry's links with other sciences (রসায়নের সাথে বিজ্ঞানের অন্যান্য শাখার সম্পর্কের চার্ট তৈরি ও উপস্থাপন)](https://offschool.site/subjects/chemistry/ch01/t05/)
  - [Topic: Importance of studying chemistry (রসায়ন পাঠের গুরুত্ব)](https://offschool.site/subjects/chemistry/ch01/t06/)
  - [Topic: A report on the importance of chemistry from the chemicals in everyday things (দৈনন্দিন ব্যবহার্য বস্তুর রাসায়নিক উপাদান চিহ্নিত করে রসায়নের গুরুত্ব নিয়ে প্রতিবেদন)](https://offschool.site/subjects/chemistry/ch01/t07/)
  - [Topic: Steps of research (গবেষণার ধাপসমূহ)](https://offschool.site/subjects/chemistry/ch01/t08/)
  - [Topic: Steps of investigation and research in chemistry: planning an investigation of water pollution in a local pond (রসায়নে অনুসন্ধান ও গবেষণার ধাপ: স্থানীয় জলাশয়ের পানি দূষণ অনুসন্ধানের পরিকল্পনা)](https://offschool.site/subjects/chemistry/ch01/t09/)
  - [Topic: Planning investigative work (অনুসন্ধানমূলক কাজের পরিকল্পনা)](https://offschool.site/subjects/chemistry/ch01/t10/)
  - [Topic: Forming and testing a hypothesis about the nature (acidity or basicity) of the pond water (জলাশয়ের পানির প্রকৃতি (অম্লত্ব বা ক্ষারকত্ব) নিয়ে অনুমিত সিদ্ধান্ত গঠন ও পরীক্ষণ)](https://offschool.site/subjects/chemistry/ch01/t11/)
  - [Topic: Safety measures and warning symbols in storing and using chemicals (রাসায়নিক দ্রব্য সংরক্ষণ ও ব্যবহারে সতর্কতামূলক ব্যবস্থা এবং সতর্কতামূলক চিহ্ন)](https://offschool.site/subjects/chemistry/ch01/t12/)
  - [Simulation: Safety precautions in diluting concentrated acid (ঘন এসিড লঘুকরণে নিরাপত্তা সতর্কতা)](https://offschool.site/sim/ssc.chemistry.ch01.lab-safety/): In the school chemistry laboratory, the teacher asked students to prepare a dilute solution by mixing 10 mL of concentrated sulfuric acid (H₂SO₄) into 50 mL of water. A beaker, measuring cylinder, distilled water, a fume hood, and PPE (goggles, apron, gloves) are available. What is the safest and correct procedure for mixing the two liquids in the beaker?
  - [Simulation: Tannery pond and acidity hypothesis (ট্যানারির জলাশয় ও অম্লত্ব অনুসন্ধান)](https://offschool.site/sim/ssc.chemistry.ch01.tannery-pond-hypothesis/): Class 10 students planned an inquiry to investigate whether industrial acid waste has contaminated a pond near the Savar tannery estate. They hypothesized that the pond water has turned acidic due to tannery effluent. In the lab, a 50 mL water sample with an acid concentration of 0.02 mol/L was placed in a conical flask. An indicator was added, and 0.1 mol/L sodium hydroxide (NaOH) base solution was added drop by drop from a burette. How many mL of base solution are needed to completely neutralise the water sample (at equivalence point)?
- [Chapter 2: States of Matter (পদার্থের অবস্থা)](https://offschool.site/subjects/chemistry/ch02/)
  - [Topic: Postulates of the kinetic theory of particles (পদার্থকণার গতিতত্ত্বের স্বীকার্য)](https://offschool.site/subjects/chemistry/ch02/t01/)
  - [Topic: Observing particles in motion: dust in a beam of light and pollen in water (কণার বিচরণ পর্যবেক্ষণ: আলোয় ধূলিকণা ও পানিতে ফুলের রেণু)](https://offschool.site/subjects/chemistry/ch02/t02/)
  - [Topic: Kinetic theory and the physical states of matter (কণার গতিতত্ত্ব ও পদার্থের ভৌত অবস্থা)](https://offschool.site/subjects/chemistry/ch02/t03/)
  - [Topic: Analysing diffusion and effusion in everyday events (বাস্তব ঘটনায় ব্যাপন ও নিঃসরণের বিশ্লেষণ)](https://offschool.site/subjects/chemistry/ch02/t04/)
  - [Topic: Diffusion and effusion (ব্যাপন ও নিঃসরণ)](https://offschool.site/subjects/chemistry/ch02/t05/)
  - [Topic: Diffusion and effusion in the smell of flowers, a spray, colour in water and gases in air (ফুলের গন্ধ, স্প্রে, পানিতে রং ও বায়ুতে গ্যাসের ছড়িয়ে পড়া থেকে ব্যাপন ও নিঃসরণের ধারণা)](https://offschool.site/subjects/chemistry/ch02/t06/)
  - [Topic: Melting, vaporisation, condensation and sublimation (গলন, বাষ্পীকরণ, ঘনীভবন ও ঊর্ধ্বপাতন প্রক্রিয়া)](https://offschool.site/subjects/chemistry/ch02/t07/)
  - [Topic: Heating and cooling wax, ice cream, water and naphthalene (মোম, আইসক্রিম, পানি ও ন্যাপথালিনে তাপ দেওয়া ও ঠান্ডা করা)](https://offschool.site/subjects/chemistry/ch02/t08/)
  - [Topic: Effect of heat on the physical state of matter (পদার্থের ভৌত অবস্থার উপর তাপের প্রভাব)](https://offschool.site/subjects/chemistry/ch02/t09/)
  - [Topic: The rate of diffusion rises with temperature (তাপমাত্রা বৃদ্ধিতে ব্যাপন হার বৃদ্ধি)](https://offschool.site/subjects/chemistry/ch02/t10/)
  - [Topic: Experiment: rate of diffusion of potassium permanganate in cold, normal and hot water (পরীক্ষা: ঠান্ডা, স্বাভাবিক ও গরম পানিতে পটাশিয়াম পারম্যাঙ্গানেটের ব্যাপন হার)](https://offschool.site/subjects/chemistry/ch02/t11/)
  - [Topic: Melting of ice and sublimation of naphthalene and camphor (বরফের গলন এবং ন্যাপথালিন ও কর্পূরের ঊর্ধ্বপাতন)](https://offschool.site/subjects/chemistry/ch02/t12/)
  - [Topic: Distillation (পাতন)](https://offschool.site/subjects/chemistry/ch02/t17/)
  - [Topic: Experiment: melting of wax and condensation (পরীক্ষা: মোমের গলন ও ঘনীভবন প্রক্রিয়া)](https://offschool.site/subjects/chemistry/ch02/t13/)
  - [Topic: Using a thermometer (থার্মোমিটারের ব্যবহার)](https://offschool.site/subjects/chemistry/ch02/t14/)
  - [Topic: Measuring the temperature of chemical substances (রাসায়নিক দ্রব্যের তাপমাত্রা নির্ণয়)](https://offschool.site/subjects/chemistry/ch02/t15/)
  - [Topic: Motivational talk (উদ্বুদ্ধমূলক বক্তব্য)](https://offschool.site/subjects/chemistry/ch02/t16/)
  - [Simulation: Diffusion of ammonia and hydrochloric acid (অ্যামোনিয়া ও হাইড্রোক্লোরিক অ্যাসিডের ব্যাপন)](https://offschool.site/sim/ssc.chemistry.ch02.ammonia-meets-hcl/): In a 100 cm glass tube with ammonia (NH₃, molar mass 17) at both ends, both gases diffuse at the same rate and meet right at the middle (50 cm). Now, keeping ammonia at the left end, cotton soaked in hydrochloric acid (HCl, molar mass 36.5) is placed at the right end. As both gases diffuse toward each other, how far from the NH₃ end will the white ring of solid NH₄Cl form?
  - [Simulation: Hot khichuri aroma and diffusion (গরম খিচুড়ির সুবাস ও ব্যাপন)](https://offschool.site/sim/ssc.chemistry.ch02.hot-khichuri-diffusion/): On a rainy day, the aroma of hot khichuri cooking in the kitchen quickly spreads to the living room. But cold food from the fridge cannot be smelled unless you get close. In a 100 cm glass tube at 25 °C, ammonia (NH₃) gas particles move at 661 m/s. If the tube is heated to 100 °C, like steaming hot food, what will happen to the particle speed and diffusion rate?
  - [Simulation: State changes of naphthalene in the particle model (কণার গতিতত্ত্বে ন্যাফথালিনের অবস্থা পরিবর্তন)](https://offschool.site/sim/ssc.chemistry.ch02.naphthalene-states/): White naphthalene balls (melting point 80 °C, boiling point 218 °C) kept in cupboards stay solid at room temperature (25 °C). Kinetic theory states heating boosts kinetic energy and weakens intermolecular attraction. If naphthalene in a test tube is heated to 85 °C, what physical state will it be in?
  - [Simulation: Why do pollen grains dance in water? (পানিতে পরাগরেণু নাচে কেন?)](https://offschool.site/sim/ssc.chemistry.ch02.pollen-dance/): Looking through a microscope at pollen grains floating in a drop of water, Ayesha sees them jiggling and wandering at random, though the water is perfectly still. Dust in a sunbeam through the window dances the same way. If the water is warmed, how will the pollen move?
  - [Simulation: Which thermometer for which job? (কোন জিনিস মাপতে কোন থার্মোমিটার?)](https://offschool.site/sim/ssc.chemistry.ch02.right-thermometer/): In the chemistry lab Nipa must measure three things: a freezing mixture of ice and salt, boiling water and hot frying oil. A clinical thermometer is at hand, and she thinks a thermometer is a thermometer, so it will do for everything. What happens if she puts the clinical thermometer in boiling water?
- [Chapter 3: Structure of Matter (পদার্থের গঠন)](https://offschool.site/subjects/chemistry/ch03/)
  - [Topic: Elements and compounds (মৌলিক ও যৌগিক পদার্থ)](https://offschool.site/subjects/chemistry/ch03/t16/)
  - [Topic: Atoms and molecules (পরমাণু ও অণু)](https://offschool.site/subjects/chemistry/ch03/t17/)
  - [Topic: Symbols of elements (মৌলের প্রতীক)](https://offschool.site/subjects/chemistry/ch03/t18/)
  - [Topic: Chemical formulae (রাসায়নিক সংকেত)](https://offschool.site/subjects/chemistry/ch03/t19/)
  - [Topic: Development of the idea of the atom (পরমাণু সম্পর্কে ধারণার বিকাশ)](https://offschool.site/subjects/chemistry/ch03/t01/)
  - [Topic: Group work: cutting a green leaf smaller and smaller to reach the idea of the atom (দলগত কাজ: সবুজ পাতা ক্রমশ ক্ষুদ্র করে কেটে পরমাণুর ধারণা)](https://offschool.site/subjects/chemistry/ch03/t02/)
  - [Topic: Fundamental and stable particles (মৌলিক ও স্থায়ী কণিকা)](https://offschool.site/subjects/chemistry/ch03/t03/)
  - [Topic: Properties of the proton, electron and neutron (প্রোটন, ইলেকট্রন ও নিউট্রনের বৈশিষ্ট্য)](https://offschool.site/subjects/chemistry/ch03/t04/)
  - [Topic: Atomic number, mass number and relative atomic mass (পারমাণবিক সংখ্যা, ভর সংখ্যা ও আপেক্ষিক পারমাণবিক ভর)](https://offschool.site/subjects/chemistry/ch03/t05/)
  - [Topic: Calculating relative molecular mass from relative atomic mass (আপেক্ষিক পারমাণবিক ভর থেকে আপেক্ষিক আণবিক ভর হিসাব)](https://offschool.site/subjects/chemistry/ch03/t06/)
  - [Topic: Counting the electrons, protons and neutrons of an atom (পরমাণুর ইলেকট্রন, প্রোটন ও নিউট্রন হিসাব)](https://offschool.site/subjects/chemistry/ch03/t07/)
  - [Topic: Isotopes (আইসোটোপ)](https://offschool.site/subjects/chemistry/ch03/t08/)
  - [Topic: Finding the number of neutrons from atomic number and mass number (পারমাণবিক সংখ্যা ও ভর সংখ্যা থেকে নিউট্রন সংখ্যা নির্ণয়)](https://offschool.site/subjects/chemistry/ch03/t09/)
  - [Topic: Precautions in using isotopes in medicine, agriculture and power (চিকিৎসা, কৃষি ও বিদ্যুৎ ক্ষেত্রে আইসোটোপ ব্যবহারের সতর্কতা)](https://offschool.site/subjects/chemistry/ch03/t10/)
  - [Topic: Problems that isotopes can cause (আইসোটোপ যেসব সমস্যা সৃষ্টি করতে পারে)](https://offschool.site/subjects/chemistry/ch03/t11/)
  - [Topic: Atomic models (পরমাণু মডেল)](https://offschool.site/subjects/chemistry/ch03/t12/)
  - [Topic: Comparing the Rutherford and Bohr models of the atom (রাদারফোর্ড ও বোর পরমাণু মডেলের তুলনা)](https://offschool.site/subjects/chemistry/ch03/t13/)
  - [Topic: Arrangement of electrons in energy levels (শক্তিস্তরে ইলেকট্রন বিন্যাস)](https://offschool.site/subjects/chemistry/ch03/t14/)
  - [Topic: The 2n² rule and the capacity of the K, L, M and N shells (ইলেকট্রন বিন্যাসের 2n² সূত্র এবং K, L, M, N শক্তিস্তরে ইলেকট্রন ধারণ ক্ষমতা)](https://offschool.site/subjects/chemistry/ch03/t15/)
  - [Simulation: Atomic structure and isotopes (পরমাণুর গঠন ও আইসোটোপ)](https://offschool.site/sim/ssc.chemistry.ch03.build-an-atom/): The primary constituent of pencil graphite and charcoal is carbon (C). A standard carbon atom has 6 protons and 6 neutrons in its nucleus, with 6 electrons orbiting in energy levels, giving a mass number of 12. If 1 extra neutron is added to this nucleus to make 7 neutrons, what happens to the atom, does the element change or remain carbon, and what will its mass number be?
  - [Simulation: Filling electron shells: the 2n² rule and Bohr model (শক্তিস্তরে ইলেকট্রন বিন্যাস: ২n² নিয়ম ও বোর মডেল)](https://offschool.site/sim/ssc.chemistry.ch03.fill-the-shells/): In Bangladesh, red muriate of potash (MOP) fertilizer is widely used on paddy fields to boost crop yield and drought resistance. Its key element is potassium (K) with atomic number 19, meaning a neutral atom has 19 electrons. According to the Bohr model, the maximum electron capacity of each principal energy level follows the 2n² rule. Under this rule, the 1st shell K (n = 1) holds up to 2 electrons, the 2nd shell L (n = 2) up to 8, and the 3rd shell M (n = 3) up to 18. After 2 + 8 = 10 electrons fill the first two shells, 9 electrons remain. How are these 19 electrons arranged across the K, L, M, and N shells in a potassium atom?
  - [Simulation: How heavy is a glucose molecule? (গ্লুকোজের একটি অণু কত ভারী?)](https://offschool.site/sim/ssc.chemistry.ch03.glucose-molecular-mass/): The doctor tells Rashed's grandmother to take glucose with her saline. The packet says C₆H₁₂O₆. Rashed knows the relative atomic masses: carbon 12, hydrogen 1, oxygen 16. How heavy is one glucose molecule, that is, what is its relative molecular mass?
  - [Simulation: Why did alpha particles bounce off gold foil? (সোনার পাত থেকে আলফা কণা ফিরে এলো কেন?)](https://offschool.site/sim/ssc.chemistry.ch03.gold-foil-surprise/): In 1909, Rutherford's students fired alpha particles at very thin gold foil. The idea of the day was Thomson's model: an atom is a soft ball of positive charge with electrons stuck in it. By that picture every particle should pass almost straight through. What did they actually find?
  - [Simulation: Why does hydrogen glow in set colours? (হাইড্রোজেন কেন নির্দিষ্ট রঙের আলো দেয়?)](https://offschool.site/sim/ssc.chemistry.ch03.hydrogen-colour-lines/): Pass electricity through a tube of hydrogen and it glows; through a prism you see not a full rainbow but a few separate lines: red, cyan, blue and violet. In Bohr's model, an electron dropping from level n = 3 to n = 2 gives the red line. What colour comes from a drop from n = 4 to n = 2?
- [Chapter 4: Periodic Table (পর্যায় সারণি)](https://offschool.site/subjects/chemistry/ch04/)
  - [Topic: Development of the periodic table (পর্যায় সারণির বিকাশ)](https://offschool.site/subjects/chemistry/ch04/t01/)
  - [Topic: Background to the development of the periodic table (পর্যায় সারণির বিকাশের পটভূমি)](https://offschool.site/subjects/chemistry/ch04/t02/)
  - [Topic: Locating an element in the periodic table from its electron configuration (ইলেকট্রন বিন্যাস থেকে পর্যায় সারণিতে মৌলের অবস্থান নির্ণয়)](https://offschool.site/subjects/chemistry/ch04/t03/)
  - [Topic: Relation of electron configuration to the group and period of an element (ইলেকট্রন বিন্যাসের সাথে মৌলের শ্রেণি ও পর্যায়ের সম্পর্ক)](https://offschool.site/subjects/chemistry/ch04/t04/)
  - [Topic: Periodic properties of elements (মৌলের পর্যায়বৃত্ত ধর্ম)](https://offschool.site/subjects/chemistry/ch04/t05/)
  - [Topic: Common features of a group and predicting an element's physical and chemical properties (একই শ্রেণির মৌলের সাধারণ বৈশিষ্ট্য এবং মৌলের সম্ভাব্য ভৌত ও রাসায়নিক ধর্ম)](https://offschool.site/subjects/chemistry/ch04/t06/)
  - [Topic: Special names of groups: alkali metals, alkaline earth metals, coinage metals, halogens, noble gases, transition elements (বিভিন্ন শ্রেণির মৌলের বিশেষ নাম: ক্ষার ধাতু, মৃৎক্ষার ধাতু, মুদ্রা ধাতু, হ্যালোজেন, নিষ্ক্রিয় গ্যাস, অবস্থান্তর মৌল)](https://offschool.site/subjects/chemistry/ch04/t07/)
  - [Topic: Advantages of the periodic table (পর্যায় সারণির সুবিধা)](https://offschool.site/subjects/chemistry/ch04/t08/)
  - [Topic: The modern periodic table (আধুনিক পর্যায় সারণি)](https://offschool.site/subjects/chemistry/ch04/t09/)
  - [Topic: Similar properties of compounds of elements in the same group (একই শ্রেণির মৌলের যৌগের একই ধরনের ধর্ম)](https://offschool.site/subjects/chemistry/ch04/t10/)
  - [Topic: Experiment: testing the gas given off when carbonates react with dilute acid (পরীক্ষা: কার্বনেট লবণের সাথে লঘু এসিডের বিক্রিয়ায় উৎপন্ন গ্যাস পরীক্ষা)](https://offschool.site/subjects/chemistry/ch04/t11/)
  - [Simulation: Families of the periodic table: alkali metals and halogens (পর্যায় সারণির পরিবার: ক্ষারধাতু ও হ্যালোজেন)](https://offschool.site/sim/ssc.chemistry.ch04.alkali-metal-family/): In the chemistry lab, sodium (Na, atomic number 11) is stored under kerosene to protect it from air and moisture. Its first ionization energy is 496 kJ/mol. The next alkali metal in group 1, potassium (K, atomic number 19), reacts even more violently with water. A potassium atom has 19 protons and 4 electron shells (2, 8, 8, 1). Based on this: which element, sodium or potassium, has the lower first ionization energy?
  - [Simulation: Eggshell in vinegar: which gas is bubbling? (ডিমের খোসা আর ভিনেগার: কোন গ্যাসের বুদবুদ?)](https://offschool.site/sim/ssc.chemistry.ch04.eggshell-vinegar-gas/): In the kitchen, Mitu drops a piece of eggshell into vinegar and sees a steady stream of tiny bubbles rising from it. Her brother says it must be hydrogen, because acids give off hydrogen. Mitu decides to lead the gas through a tube into limewater to test it. What will she see in the limewater?
  - [Simulation: Periodic trends and atomic radius (পর্যায়বৃত্ত ধর্ম ও পারমাণবিক আকার)](https://offschool.site/sim/ssc.chemistry.ch04.periodic-trends/): The primary component of our daily table salt is sodium (Na, atomic number 11) and chlorine (Cl, atomic number 17). In the periodic table, both elements belong to Period 3. A sodium atom has an atomic radius of 166 pm. A chlorine atom has 17 protons and 17 electrons, more protons and electrons than sodium. Based on this, which atom has a larger atomic size?
- [Chapter 5: Chemical Bond (রাসায়নিক বন্ধন)](https://offschool.site/subjects/chemistry/ch05/)
  - [Topic: Valence electrons (যোজ্যতা ইলেকট্রন)](https://offschool.site/subjects/chemistry/ch05/t01/)
  - [Topic: Valence electrons from the electrons of the outermost shell (বহিঃস্থ স্তরের ইলেকট্রন থেকে যোজ্যতা ইলেকট্রনের ধারণা)](https://offschool.site/subjects/chemistry/ch05/t02/)
  - [Topic: Valency (যোজনী বা যোজ্যতা)](https://offschool.site/subjects/chemistry/ch05/t23/)
  - [Topic: Radicals and their valencies (যৌগমূলক ও তাদের যোজনী)](https://offschool.site/subjects/chemistry/ch05/t24/)
  - [Topic: Chemical formula of compounds (যৌগের রাসায়নিক সংকেত)](https://offschool.site/subjects/chemistry/ch05/t25/)
  - [Topic: Molecular formula and structural formula (আণবিক সংকেত ও গাঠনিক সংকেত)](https://offschool.site/subjects/chemistry/ch05/t26/)
  - [Topic: Noble gases and their stability (নিষ্ক্রিয় গ্যাস এবং এর স্থিতিশীলতা)](https://offschool.site/subjects/chemistry/ch05/t03/)
  - [Topic: Explaining the stability of noble gases with the octet and duet rules (অষ্টক ও দুই-এর নিয়মের সাহায্যে নিষ্ক্রিয় গ্যাসের স্থিতিশীলতার ব্যাখ্যা)](https://offschool.site/subjects/chemistry/ch05/t04/)
  - [Topic: Group work: chemical bonds of several compounds in dot-and-cross diagrams (দলগত কাজ: ডট-ক্রস চিত্রে বিভিন্ন যৌগের রাসায়নিক বন্ধন)](https://offschool.site/subjects/chemistry/ch05/t05/)
  - [Topic: The octet rule and the duet rule (অষ্টক ও দুই-এর নিয়ম)](https://offschool.site/subjects/chemistry/ch05/t06/)
  - [Topic: Chemical bond (রাসায়নিক বন্ধন)](https://offschool.site/subjects/chemistry/ch05/t07/)
  - [Topic: Atoms form bonds to reach a noble gas electron configuration (পরমাণু নিষ্ক্রিয় গ্যাসের ইলেকট্রন বিন্যাস অর্জনের জন্য বন্ধন গঠন করে)](https://offschool.site/subjects/chemistry/ch05/t08/)
  - [Topic: Cations and anions (ক্যাটায়ন ও অ্যানায়ন)](https://offschool.site/subjects/chemistry/ch05/t09/)
  - [Topic: Why cations and anions form, in the light of the octet and duet rules (অষ্টক ও দুই-এর নিয়মের আলোকে ক্যাটায়ন ও অ্যানায়ন সৃষ্টির কারণ)](https://offschool.site/subjects/chemistry/ch05/t10/)
  - [Topic: Ionic bond (আয়নিক বন্ধন)](https://offschool.site/subjects/chemistry/ch05/t11/)
  - [Topic: Ions of opposite charge joining to form an ionic bond, and its definition (বিপরীত আধানের আয়ন যুক্ত হয়ে আয়নিক বন্ধন গঠন ও এর সংজ্ঞা)](https://offschool.site/subjects/chemistry/ch05/t12/)
  - [Topic: Covalent bond (সমযোজী বন্ধন)](https://offschool.site/subjects/chemistry/ch05/t13/)
  - [Topic: Reaching a noble gas configuration by sharing electrons, and the definition of a covalent bond (ইলেকট্রন শেয়ারের মাধ্যমে নিষ্ক্রিয় গ্যাসের ইলেকট্রন বিন্যাস অর্জন ও সমযোজী বন্ধনের সংজ্ঞা)](https://offschool.site/subjects/chemistry/ch05/t14/)
  - [Topic: Group work: comparing table salt (NaCl) and sugar (C₁₂H₂₂O₁₁) on heating (দলগত কাজ: খাদ্য লবণ (NaCl) ও চিনি (C₁₂H₂₂O₁₁) উত্তপ্ত করে তুলনা)](https://offschool.site/subjects/chemistry/ch05/t15/)
  - [Topic: Properties of ionic and covalent compounds (আয়নিক ও সমযোজী যৌগের বৈশিষ্ট্য)](https://offschool.site/subjects/chemistry/ch05/t16/)
  - [Topic: Group work: comparing ionic and covalent compounds by dissolving them in water (দলগত কাজ: আয়নিক ও সমযোজী যৌগ পানিতে দ্রবীভূত করে তুলনা)](https://offschool.site/subjects/chemistry/ch05/t17/)
  - [Topic: Group work: testing the conductivity of salt and sugar solutions with a battery and a bulb (দলগত কাজ: লবণ ও চিনির দ্রবণের বিদ্যুৎ পরিবাহিতা পরীক্ষা)](https://offschool.site/subjects/chemistry/ch05/t18/)
  - [Topic: Structure of metals and the metallic bond (ধাতুর গঠন ও ধাতব বন্ধন)](https://offschool.site/subjects/chemistry/ch05/t19/)
  - [Topic: Metallic bond (ধাতব বন্ধন)](https://offschool.site/subjects/chemistry/ch05/t20/)
  - [Topic: Why metals conduct electricity (ধাতুর বিদ্যুৎ পরিবাহিতার কারণ)](https://offschool.site/subjects/chemistry/ch05/t21/)
  - [Topic: Identifying ionic and covalent compounds among locally available substances (স্থানীয়ভাবে সহজপ্রাপ্য দ্রব্যের মধ্যে আয়নিক ও সমযোজী যৌগ শনাক্তকরণ)](https://offschool.site/subjects/chemistry/ch05/t22/)
  - [Simulation: Build a bond: where do the electrons go? (বন্ধন গড়ো: ইলেকট্রন কোথায় যায়?)](https://offschool.site/sim/ssc.chemistry.ch05.build-a-bond/): In the school lab a magnesium ribbon burns with a blinding white light and leaves a white powder: magnesium oxide (MgO). Mg has 2 electrons in its outer shell, O has 6. Both atoms want a full outer shell like a noble gas. Where do the electrons go?
  - [Simulation: Dot-and-cross workshop: building covalent molecules (ডট-ক্রস কর্মশালা: সমযোজী অণুর গঠন)](https://offschool.site/sim/ssc.chemistry.ch05.dot-and-cross-workshop/): In classroom group work, the teacher asked students to draw covalent molecules using dot-and-cross diagrams. The main component of natural gas is methane. A carbon atom (C) has 4 valence electrons in its outer shell and a hydrogen atom (H) has 1. Both atoms want to achieve stable noble gas electron configurations: an octet of 8 for carbon and a duplet of 2 for hydrogen. How many hydrogen atoms are needed to bond with one carbon atom to form a stable methane molecule?
  - [Simulation: Metallic bonding: how electricity flows through wires (ধাতব বন্ধন: তারের ভেতর বিদ্যুৎ চলে কীভাবে?)](https://offschool.site/sim/ssc.chemistry.ch05.metal-electron-sea/): In household electrical wiring and school science labs, metals like copper or aluminium are used as wires. As soon as a switch is closed, electricity flows through the solid metal wire. In contrast, table salt (NaCl), although made of ions, conducts no electricity as a solid: it only conducts when melted or dissolved in water. How does a metal conduct electricity in its solid state without being melted? What happens to the atoms and electrons inside a metal?
  - [Simulation: Pressure cooker oxide layer: formula from valency (প্রেশার কুকারের অক্সাইড স্তর: যোজনী থেকে সংকেত)](https://offschool.site/sim/ssc.chemistry.ch05.pressure-cooker-oxide-formula/): Pressure cookers in our kitchens are made of aluminium. Reacting with oxygen in the air, a thin, tough protective layer of aluminium oxide forms on its surface, preventing further corrosion. Aluminium (Al) has a valency of 3 and oxygen (O) has a valency of 2. Following the criss-cross rule of valencies, what is the chemical formula of aluminium oxide?
  - [Simulation: Ionic and covalent bonds: Table salt and chlorine gas (আয়নিক ও সমযোজী বন্ধন: খাদ্য লবণ ও ক্লোরিন গ্যাস)](https://offschool.site/sim/ssc.chemistry.ch05.salt-bond/): In table salt (NaCl) used daily in our cooking, a sodium atom (Na, 1 valence electron) transfers its valence electron completely to a chlorine atom (Cl, 7 valence electrons). This forms Na⁺ and Cl⁻ ions that attract each other to create an ionic bond. On the other hand, in chlorine gas (Cl₂) used for water purification, both atoms are chlorine (non-metals) and each has 7 valence electrons in its outer shell. Neither atom can give up electrons. What type of chemical bond forms between two chlorine atoms when they combine into a Cl₂ molecule?
  - [Simulation: Salt versus sugar: Properties of ionic and covalent compounds (খাদ্য লবণ বনাম চিনি: আয়নিক ও সমযোজী যৌগের বৈশিষ্ট্য)](https://offschool.site/sim/ssc.chemistry.ch05.salt-versus-sugar-properties/): In the school science lab, an electric circuit with a battery and a bulb tests the conductivity of two solutions: table salt (NaCl) in one beaker and methane (CH₄) in another. Table salt melts at 801 °C and methane melts at -182 °C. Which substance will conduct electricity and light the bulb when dissolved in water?
- [Chapter 6: Concept of Mole and Chemical Counting (মোলের ধারণা ও রাসায়নিক গণনা)](https://offschool.site/subjects/chemistry/ch06/)
  - [Topic: The mole and Avogadro's number (মোল ও অ্যাভোগেড্রো সংখ্যা)](https://offschool.site/subjects/chemistry/ch06/t01/)
  - [Topic: The mole as a counting unit (like a dozen) (গণনার একক হিসেবে মোল (ডজন ও হালির মতো))](https://offschool.site/subjects/chemistry/ch06/t02/)
  - [Topic: Molar solution, or molarity (মোলার দ্রবণ বা মোলারিটি)](https://offschool.site/subjects/chemistry/ch06/t03/)
  - [Topic: Group work: preparing a solution of known concentration (NaCl, glucose or copper sulphate) (দলগত কাজ: নির্দিষ্ট ঘনমাত্রার দ্রবণ তৈরি (NaCl, গ্লুকোজ বা তুঁতে))](https://offschool.site/subjects/chemistry/ch06/t05/)
  - [Topic: Percentage composition of the elements in a compound (যৌগে উপস্থিত মৌলের শতকরা সংযুতি)](https://offschool.site/subjects/chemistry/ch06/t06/)
  - [Topic: Empirical formula and molecular formula (স্থূল সংকেত ও আণবিক সংকেত)](https://offschool.site/subjects/chemistry/ch06/t08/)
  - [Topic: Working out empirical and molecular formulas from percentage composition (শতকরা সংযুতি থেকে স্থূল সংকেত ও আণবিক সংকেত গণনা)](https://offschool.site/subjects/chemistry/ch06/t09/)
  - [Topic: Chemical equations (রাসায়নিক সমীকরণ)](https://offschool.site/subjects/chemistry/ch06/t10/)
  - [Topic: Writing and balancing an equation from its reactants and products (বিক্রিয়ক ও উৎপাদ থেকে রাসায়নিক সমীকরণ লেখা ও সমতা করা)](https://offschool.site/subjects/chemistry/ch06/t11/)
  - [Topic: Finding the amount of product from the quantitative meaning of an equation (রাসায়নিক সমীকরণের মাত্রিক তাৎপর্য ব্যবহার করে উৎপাদের পরিমাণ নির্ণয়)](https://offschool.site/subjects/chemistry/ch06/t12/)
  - [Topic: Calculating the mass of product from the mass of reactant using the mole (মোলের ধারণার সাহায্যে বিক্রিয়কের ভর থেকে উৎপাদের ভর গণনা)](https://offschool.site/subjects/chemistry/ch06/t13/)
  - [Topic: Limiting reactant (লিমিটিং বিক্রিয়ক)](https://offschool.site/subjects/chemistry/ch06/t16/)
  - [Topic: Calculation of the percentage of yield (উৎপাদের শতকরা পরিমাণ হিসাব)](https://offschool.site/subjects/chemistry/ch06/t17/)
  - [Topic: Water of crystallisation (কেলাস পানি)](https://offschool.site/subjects/chemistry/ch06/t14/)
  - [Topic: Group work: finding the percentage of water of crystallisation in blue vitriol in the laboratory (দলগত কাজ: ল্যাবরেটরিতে তুঁতের কেলাস পানির শতকরা পরিমাণ নির্ণয়)](https://offschool.site/subjects/chemistry/ch06/t15/)
  - [Simulation: How much of blue vitriol is water? (তুঁতের কতটা আসলে পানি?)](https://offschool.site/sim/ssc.chemistry.ch06.blue-vitriol-crystal-water/): In the chemistry lab, Sakib puts 5 grams of blue vitriol in a crucible and starts heating it. The blue crystals slowly turn into a white powder and the balance reading falls. Dry as they looked, the crystals held water. What percentage of blue vitriol's mass is water?
  - [Simulation: Which fertiliser carries the most nitrogen? (কোন সারে নাইট্রোজেন সবচেয়ে বেশি?)](https://offschool.site/sim/ssc.chemistry.ch06.fertiliser-nitrogen-share/): In a shop in Dinajpur, a farmer sees three nitrogen fertilisers: urea, ammonium sulfate and ammonium nitrate. Every bag weighs 50 kg. Which bag holds the most nitrogen?
  - [Simulation: How many grams for a 0.1 molar blue vitriol solution? (০.১ মোলার তুঁতে দ্রবণ বানাতে কত গ্রাম?)](https://offschool.site/sim/ssc.chemistry.ch06.making-a-molar-solution/): Lab assistant Rumana must make 250 mL of 0.1 molar copper sulfate solution for tomorrow's class. She has blue vitriol crystals, CuSO₄·5H₂O. How many grams should she weigh out and make up to the mark in a 250 mL volumetric flask?
  - [Simulation: Mole concept and chemical calculation (মোলের ধারণা ও রাসায়নিক গণনা)](https://offschool.site/sim/ssc.chemistry.ch06.mole-counting/): Just as rice in a grocery store is weighed on a scale rather than counted grain by grain, atoms and molecules are invisible to the naked eye, so chemists count them by measuring mass in moles. According to the balanced equation (2H₂ + O₂ → 2H₂O), 2 g of hydrogen gas (1 mole or 6.02 × 10²³ molecules) reacts completely with oxygen to produce 18 g of water. If you react 4 g of hydrogen gas, what mass of water will be produced?
  - [Simulation: Same percentages, different compounds? (একই শতকরা সংযুতি, তবু ভিন্ন যৌগ?)](https://offschool.site/sim/ssc.chemistry.ch06.vinegar-and-glucose-formula/): Two samples analysed in the lab give the same result: carbon 40.0%, hydrogen 6.7%, oxygen 53.3%. One is ethanoic acid from vinegar (molar mass 60), the other glucose (molar mass 180). Tamanna says that if the percentages are the same, the compound must be the same. Is she right?
- [Chapter 7: Chemical Reactions (রাসায়নিক বিক্রিয়া)](https://offschool.site/subjects/chemistry/ch07/)
  - [Topic: Physical change and chemical change (ভৌত পরিবর্তন ও রাসায়নিক পরিবর্তন)](https://offschool.site/subjects/chemistry/ch07/t01/)
  - [Topic: Classification of chemical reactions (precipitation, acid-base neutralisation and redox) (রাসায়নিক বিক্রিয়ার শ্রেণিবিভাগ (অধঃক্ষেপণ, অম্ল-ক্ষার প্রশমন ও জারণ-বিজারণ))](https://offschool.site/subjects/chemistry/ch07/t02/)
  - [Topic: Special types of chemical reactions (বিশেষ ধরনের রাসায়নিক বিক্রিয়া)](https://offschool.site/subjects/chemistry/ch07/t13/)
  - [Topic: Le Chatelier's principle (লা-শাতেলিয়ারের নীতি)](https://offschool.site/subjects/chemistry/ch07/t03/)
  - [Topic: Redox reactions (জারণ-বিজারণ বিক্রিয়া)](https://offschool.site/subjects/chemistry/ch07/t04/)
  - [Topic: Some chemical reactions in everyday settings (বাস্তবে বিভিন্ন ক্ষেত্রে সংঘটিত কিছু রাসায়নিক বিক্রিয়া)](https://offschool.site/subjects/chemistry/ch07/t05/)
  - [Topic: Homework: the effect of chemical reactions on things used every day (বাড়ির কাজ: দৈনন্দিন ব্যবহৃত দ্রব্যের উপর রাসায়নিক বিক্রিয়ার প্রভাব)](https://offschool.site/subjects/chemistry/ch07/t06/)
  - [Topic: Preventing and controlling harmful reactions: rusting of iron and how to stop it (ক্ষতিকর রাসায়নিক বিক্রিয়া রোধ ও নিয়ন্ত্রণ: লোহার মরিচা ও তা রোধের উপায়)](https://offschool.site/subjects/chemistry/ch07/t07/)
  - [Topic: Comparing the rates of reactions in nature and in the laboratory (প্রকৃতিতে ও গবেষণাগারে সংঘটিত রাসায়নিক বিক্রিয়ার হারের তুলনা)](https://offschool.site/subjects/chemistry/ch07/t08/)
  - [Topic: Group work: comparing the rate of a reaction in cold and hot water (দলগত কাজ: ঠান্ডা ও গরম পানিতে বিক্রিয়ার হারের তুলনা)](https://offschool.site/subjects/chemistry/ch07/t09/)
  - [Topic: Group work: adding lime water to lemon juice and testing with litmus paper (দলগত কাজ: লেবুর রসে চুনের পানি যোগ করে লিটমাস কাগজে পরীক্ষা)](https://offschool.site/subjects/chemistry/ch07/t10/)
  - [Topic: Precipitation reaction of blue vitriol with an alkali (তুঁতে ও ক্ষারের অধঃক্ষেপণ বিক্রিয়া)](https://offschool.site/subjects/chemistry/ch07/t11/)
  - [Topic: Demonstrating neutralisation and precipitation reactions (অম্ল-ক্ষারক প্রশমন বিক্রিয়া এবং অধঃক্ষেপণ বিক্রিয়া প্রদর্শন)](https://offschool.site/subjects/chemistry/ch07/t12/)
  - [Simulation: Combustion and equation balancing of methane (গ্যাসের চুলায় মিথেনের দহন ও সমতাকরণ)](https://offschool.site/sim/ssc.chemistry.ch07.balancing-equations/): In kitchen gas stoves, methane gas (CH₄) burns in atmospheric oxygen (O₂) to produce carbon dioxide (CO₂), water vapour (H₂O), and heat. One methane molecule contains 1 carbon and 4 hydrogen atoms, burning completely to form 1 CO₂. In a chemical reaction, atoms cannot be created or destroyed. To conserve all atoms on both sides, how many O₂ molecules are needed and how many H₂O molecules are formed?
  - [Simulation: Blue vitriol and caustic soda: classifying reactions (তুঁতে আর কস্টিক সোডা: বিক্রিয়ার শ্রেণিবিভাগ)](https://offschool.site/sim/ssc.chemistry.ch07.blue-vitriol-caustic-soda/): In chemistry class Rumana takes blue vitriol solution (CuSO₄) in a test tube and adds a few drops of caustic soda solution (NaOH). Both are clear solutions, so her friend says the blue will just get a little paler, nothing more. What will actually appear in the test tube?
  - [Simulation: Silver tree and electron transfer: Redox (সিলভার ট্রি ও ইলেকট্রন স্থানান্তর: জারণ-বিজারণ)](https://offschool.site/sim/ssc.chemistry.ch07.copper-silver-tree-redox/): Jewellers recover silver by dipping copper (Cu) wire into silver nitrate (AgNO₃) solution. A glittering 'silver tree' of crystals grows on the wire and the solution turns blue (Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag). Dipping 1.0 g of copper deposits 3.4 g of silver. Given that copper has atomic mass 63.5 and silver has 108, how many grams of silver will be displaced by 6.35 g (0.1 mol) of copper wire?
  - [Simulation: Preserving fish on ice and reaction rate (বরফে মাছ সংরক্ষণ ও বিক্রিয়ার হার)](https://offschool.site/sim/ssc.chemistry.ch07.fish-on-ice-rate/): At Chandpur fish landing port on a warm day, fresh Hilsa fish cells undergo biochemical spoilage at 25 °C and 1 mol/L reactant concentration with a relative reaction rate of 1.00. To prevent rapid spoiling, fishermen cover the fish with crushed ice, bringing the temperature down to 0 °C (activation energy 50 kJ/mol). What will the relative rate of this spoilage reaction be at 0 °C at the same concentration?
  - [Simulation: Melting or burning: physical and chemical change (গলে যাওয়া না পুড়ে যাওয়া: ভৌত ও রাসায়নিক পরিবর্তন)](https://offschool.site/sim/ssc.chemistry.ch07.melt-or-burn/): On a winter morning Nadia puts some ice in one pan on the stove and a little sugar in another. The ice melts into water; the sugar melts, turns brown and then black, giving off steam. Nadia thinks both melted in the heat, so both are the same kind of change. Heat them in a test tube: which one makes a new substance?
  - [Simulation: Rust on coastal tin roofs: which pin survives? (উপকূলের টিনের চালে মরিচা: কোন পিন বাঁচে?)](https://offschool.site/sim/ssc.chemistry.ch07.rust-proof-nails/): On Barisal's riverbanks tin roofs and nails rust within weeks. At school Sakib puts iron pins in test tubes: one in water, one in salt water, one in boiled water sealed under a layer of oil, and one with dry calcium chloride. He adds a painted pin and a galvanised one too. He thinks any pin touching water will rust. After a week, which pins rust?
  - [Simulation: What does more pressure do in a fertiliser plant? (সার কারখানায় চাপ বাড়ালে কী হয়?)](https://offschool.site/sim/ssc.chemistry.ch07.urea-factory-ammonia/): At the Ghorashal-Palash fertiliser factory in Narsingdi, hydrogen from natural gas is combined with nitrogen from the air to make ammonia, and the ammonia is turned into urea. The reaction is reversible: ammonia also breaks back down. Engineer Nadia wonders: if the reactor's pressure is raised from 200 to 400 atmospheres, will the share of ammonia in the mixture rise?
- [Chapter 8: Chemistry and Energy (রসায়ন ও শক্তি)](https://offschool.site/subjects/chemistry/ch08/)
  - [Topic: Chemical energy (রাসায়নিক শক্তি)](https://offschool.site/subjects/chemistry/ch08/t01/)
  - [Topic: Proper use of chemical energy (রাসায়নিক শক্তির যথাযথ ব্যবহার)](https://offschool.site/subjects/chemistry/ch08/t02/)
  - [Topic: Why cities are hotter than villages (গ্রামের তুলনায় শহরে গরম বেশি কেন)](https://offschool.site/subjects/chemistry/ch08/t03/)
  - [Topic: Making electricity with zinc and copper wires in a lemon (লেবুতে জিংক ও তামার তার দিয়ে বিদ্যুৎ উৎপাদন)](https://offschool.site/subjects/chemistry/ch08/t04/)
  - [Topic: Galvanic cell (গ্যালভানিক কোষ)](https://offschool.site/subjects/chemistry/ch08/t05/)
  - [Topic: Advantages and disadvantages of batteries (ব্যাটারির সুবিধা ও অসুবিধা)](https://offschool.site/subjects/chemistry/ch08/t06/)
  - [Topic: Using electricity to drive a reaction (বিদ্যুৎ ব্যবহার করে বিক্রিয়া সংগঠন)](https://offschool.site/subjects/chemistry/ch08/t07/)
  - [Topic: Producing gases by electrolysis of water and sodium chloride (পানি ও সোডিয়াম ক্লোরাইডের তড়িৎ বিশ্লেষণে গ্যাস উৎপাদন)](https://offschool.site/subjects/chemistry/ch08/t08/)
  - [Topic: Why litmus paper changes colour during electrolysis (তড়িৎ বিশ্লেষণে লিটমাস কাগজের বর্ণ পরিবর্তনের কারণ)](https://offschool.site/subjects/chemistry/ch08/t09/)
  - [Topic: Difference between an electrolytic cell and a galvanic cell (তড়িৎ রাসায়নিক কোষ ও গ্যালভানিক কোষের পার্থক্য)](https://offschool.site/subjects/chemistry/ch08/t10/)
  - [Topic: Nuclear reactions and power generation (নিউক্লিয়ার বিক্রিয়া ও বিদ্যুৎ উৎপাদন)](https://offschool.site/subjects/chemistry/ch08/t11/)
  - [Topic: Generating electricity from nuclear reactions, shown with diagrams (চিত্রের সাহায্যে নিউক্লীয় বিক্রিয়া থেকে বিদ্যুৎ উৎপাদন)](https://offschool.site/subjects/chemistry/ch08/t12/)
  - [Topic: Experiment: heat change on dissolving and in chemical reactions (পদার্থ দ্রবীভূত করে ও রাসায়নিক বিক্রিয়ায় তাপের পরিবর্তন পরীক্ষা)](https://offschool.site/subjects/chemistry/ch08/t13/)
  - [Topic: Group work: testing heat change by dissolving salts and by mixing vinegar, lemon juice, lime and soda (দলগত কাজ: লবণ দ্রবীভূত করে ও দ্রবণ মিশিয়ে তাপের পরিবর্তন পরীক্ষা)](https://offschool.site/subjects/chemistry/ch08/t14/)
  - [Simulation: Why does litmus change two ways in brine? (লবণ পানিতে লিটমাস দুই রকম কেন?)](https://offschool.site/sim/ssc.chemistry.ch08.brine-litmus-colours/): A caustic soda factory in Chattogram electrolyses brine. After a field trip, Riya repeats the experiment in class with a few drops of purple litmus beside each electrode. Salt is neutral, so will the litmus change colour at all?
  - [Simulation: The sports cold pack and the heat of lime (খেলার মাঠের ঠান্ডা প্যাক আর চুনের গরম)](https://offschool.site/sim/ssc.chemistry.ch08.cold-pack-hot-pack/): When a footballer sprains an ankle, the coach squeezes a pack and within seconds it is ice-cold; inside are sal ammoniac and water. At home, pouring water on quicklime to make lime for paan makes it so hot it bubbles. Nayeem thinks mixing anything with water should warm it, so how can a pack get cold? Which substances cool water when added, and which heat it?
  - [Simulation: Lemon battery: Reactivity gap and cells in series (লেবু ব্যাটারি: সক্রিয়তার ব্যবধান ও কোষের সমবায়)](https://offschool.site/sim/ssc.chemistry.ch08.lemon-battery/): At a school science fair, Tanvir made a lemon cell by inserting a zinc (Zn) strip and a copper (Cu) strip into a lemon. A voltmeter showed that this single cell produces 1.10 V. However, lighting an LED bulb requires at least 3.00 V. If Tanvir connects 3 identical lemon cells in series with wires, what total voltage will be produced?
  - [Simulation: One cell uses electricity, the other makes it (একটি কোষ বিদ্যুৎ খায়, আরেকটি বানায়)](https://offschool.site/sim/ssc.chemistry.ch08.plating-shop-or-battery/): In Old Dhaka, a craftsman uses a battery to plate jewellery with copper in blue vitriol solution. In the next shop, Rifat sees two beakers, zinc and copper, joined by a salt bridge, with no battery, yet a bulb glows. Both have an anode and a cathode. So what is the difference?
  - [Simulation: What if the control rods are pulled out? (নিয়ন্ত্রণ দণ্ড তুলে ফেললে কী হবে?)](https://offschool.site/sim/ssc.chemistry.ch08.rooppur-control-rods/): In the Rooppur reactor, each uranium-235 nucleus that splits gives out new neutrons, which split more nuclei. Control rods made with boron soak up spare neutrons. A trainee engineer asks: if every rod is pulled right out, what happens to the chain reaction?
  - [Simulation: Split water: which gas comes out more? (পানি ভাঙলে কোন গ্যাস বেশি?)](https://offschool.site/sim/ssc.chemistry.ch08.water-splits-two-to-one/): At the science fair, Tanvir dips two carbon rods into water with a little acid and connects them to a battery. An upturned test tube full of water sits over each rod, collecting bubbles. Visitors ask: if both gases come from water, will the two tubes fill equally?
- [Chapter 9: Acid-Base Balance (এসিড-ক্ষারক সমতা)](https://offschool.site/subjects/chemistry/ch09/)
  - [Topic: Familiar acids, bases and salts (পরিচিত অম্ল, ক্ষার ও লবণ)](https://offschool.site/subjects/chemistry/ch09/t01/)
  - [Topic: Group work: identifying acids, bases and salts among familiar substances (lime, lemon juice, salt) (দলগত কাজ: পরিচিত পদার্থ থেকে অম্ল, ক্ষার ও লবণ শনাক্তকরণ (চুন, লেবুর রস, লবণ))](https://offschool.site/subjects/chemistry/ch09/t02/)
  - [Topic: Chemical properties of acids, bases and salts (অম্ল, ক্ষারক ও লবণের রাসায়নিক বৈশিষ্ট্য)](https://offschool.site/subjects/chemistry/ch09/t03/)
  - [Topic: Difference between a base and an alkali (ক্ষারক ও ক্ষারের পার্থক্য)](https://offschool.site/subjects/chemistry/ch09/t04/)
  - [Topic: Effect of acids and alkalis on materials (পদার্থের ওপর অম্ল ও ক্ষারের প্রভাব)](https://offschool.site/subjects/chemistry/ch09/t05/)
  - [Topic: Homework: leaving a staple pin in lemon juice or vinegar and observing (বাড়ির কাজ: লেবুর রস বা সিরকায় স্ট্যাপলার পিন রেখে পর্যবেক্ষণ)](https://offschool.site/subjects/chemistry/ch09/t06/)
  - [Topic: Economic importance of the effects of acids and alkalis (অম্ল ও ক্ষারের প্রভাবের অর্থনৈতিক গুরুত্ব)](https://offschool.site/subjects/chemistry/ch09/t07/)
  - [Topic: Harmful effects of using strongly acidic and alkaline substances (অধিক মাত্রার এসিডিক ও ক্ষারীয় পদার্থ ব্যবহারের ক্ষতিকর প্রভাব)](https://offschool.site/subjects/chemistry/ch09/t08/)
  - [Topic: pH and the pH scale (pH ও pH স্কেলের ধারণা)](https://offschool.site/subjects/chemistry/ch09/t09/)
  - [Topic: Importance of measuring pH: soil pH and the choice of fertiliser (pH পরিমাপের গুরুত্ব: কৃষি জমির মাটির pH ও সার নির্বাচন)](https://offschool.site/subjects/chemistry/ch09/t10/)
  - [Topic: Importance of neutralisation (প্রশমন বিক্রিয়ার গুরুত্ব)](https://offschool.site/subjects/chemistry/ch09/t11/)
  - [Topic: Lime on a bee or ant sting, and antacid for excess acidity (মৌমাছি বা পিঁপড়ার কামড়ে চুন এবং অতিরিক্ত এসিডিটিতে অ্যান্টাসিডের ব্যবহার)](https://offschool.site/subjects/chemistry/ch09/t12/)
  - [Topic: Acid rain (এসিড বৃষ্টি)](https://offschool.site/subjects/chemistry/ch09/t13/)
  - [Topic: Observing the effect of acid on stone or tissue paper (পাথর বা টিস্যু পেপারের উপর এসিডের প্রভাব পর্যবেক্ষণ)](https://offschool.site/subjects/chemistry/ch09/t14/)
  - [Topic: Homework: identifying the causes of acid rain and ways to prevent it (বাড়ির কাজ: এসিড বৃষ্টির কারণ ও প্রতিরোধের উপায় চিহ্নিতকরণ)](https://offschool.site/subjects/chemistry/ch09/t15/)
  - [Topic: The water cycle (পানি চক্র)](https://offschool.site/subjects/chemistry/ch09/t16/)
  - [Topic: Group work: a chart of the water cycle with the sea, people, plants and animals (দলগত কাজ: সমুদ্র, মানুষ, উদ্ভিদ ও প্রাণী নিয়ে পানি চক্রের চার্ট)](https://offschool.site/subjects/chemistry/ch09/t17/)
  - [Topic: Hardness of water (পানির খরতা)](https://offschool.site/subjects/chemistry/ch09/t18/)
  - [Topic: What polluted water looks like (দূষিত পানির বাস্তব চিত্র)](https://offschool.site/subjects/chemistry/ch09/t19/)
  - [Topic: Water pollution (পানি দূষণ)](https://offschool.site/subjects/chemistry/ch09/t20/)
  - [Topic: Discussion from pictures of people affected by arsenic (আর্সেনিক আক্রান্ত ব্যক্তির ছবি নিয়ে আলোচনা)](https://offschool.site/subjects/chemistry/ch09/t21/)
  - [Topic: Homework: investigating the causes of pollution in the nearest pond (বাড়ির কাজ: নিকটতম জলাশয়ের পানি দূষণের কারণ অনুসন্ধান)](https://offschool.site/subjects/chemistry/ch09/t22/)
  - [Topic: pH in finding the nature of water (পানির প্রকৃতি নির্ণয়ে pH)](https://offschool.site/subjects/chemistry/ch09/t23/)
  - [Topic: Group work: finding the nature of water from different sources with pH paper (দলগত কাজ: বিভিন্ন উৎসের পানির প্রকৃতি pH পেপার দিয়ে নির্ণয়)](https://offschool.site/subjects/chemistry/ch09/t24/)
  - [Topic: Finding the pH of solutions of different compounds (বিভিন্ন যৌগের দ্রবণের pH নির্ণয়)](https://offschool.site/subjects/chemistry/ch09/t25/)
  - [Topic: Experiment on the effect of acids and alkalis on materials (পদার্থের উপর অম্ল-ক্ষারের প্রভাব পরীক্ষা)](https://offschool.site/subjects/chemistry/ch09/t26/)
  - [Topic: Precautions before using acids and alkalis (অম্ল ও ক্ষার ব্যবহারের পূর্বে সতর্কতামূলক ব্যবস্থা)](https://offschool.site/subjects/chemistry/ch09/t27/)
  - [Topic: Posters on the horror of acid violence (এসিড সন্ত্রাসের ভয়াবহতা নিয়ে পোস্টার)](https://offschool.site/subjects/chemistry/ch09/t28/)
  - [Simulation: Brick kiln smoke and acid rain pH (ইটভাটার ধোঁয়া ও এসিড বৃষ্টির pH)](https://offschool.site/sim/ssc.chemistry.ch09.brick-kiln-acid-rain/): In Gazipur's brick kiln area, burning coal emits large amounts of sulfur and nitrogen oxides into the air. These gases dissolve in rainwater to form a dilute acid solution. A current rainwater sample has an acid concentration of 0.0002 mol/L and a pH of 3.70. Typical acid rain in the area has an acid concentration of 0.0001 mol/L and a pH of exactly 4.0. If pollution increases so that the acid concentration becomes 10 times more concentrated than the pH 4.0 rain (reaching 0.001 mol/L), what will the new pH of the rainwater be?
  - [Simulation: Telling the kitchen's acids, bases and salts apart (রান্নাঘরের এসিড, ক্ষারক আর লবণ চেনা)](https://offschool.site/sim/ssc.chemistry.ch09.kitchen-indicator-test/): Rafi's mother has stirred the lime used with paan into water to make limewater. On the table there are also lemon juice, vinegar, salt water and soap solution. Rafi will dip red litmus paper into the limewater. He thinks litmus paper always stays red and only gets darker in an acid. What colour will the paper be?
  - [Simulation: A staple pin in lemon juice: what acids and alkalis do to materials (লেবুর রসে স্ট্যাপলার পিন: এসিড ও ক্ষারের প্রভাব)](https://offschool.site/sim/ssc.chemistry.ch09.staple-pin-lemon-juice/): For homework, Tania will leave one iron staple pin in lemon juice overnight and another in vinegar. Her older sister says kitchen food can't do anything to metal, so in the morning the pins will be just as they were. What will Tania see in the morning?
  - [Simulation: Tea garden soil acidity and liming (চা বাগানের মাটির অম্লত্ব ও চুন প্রয়োগ)](https://offschool.site/sim/ssc.chemistry.ch09.tea-garden-soil-lime/): Soil testing in a tea estate in Sreemangal, Sylhet shows that the soil has become too acidic. Tea plants grow best in soil with an ideal pH of 5.5 to 6.5. To reduce soil acidity, farmers add lime. In the lab, 25 mL of soil water (modeled as a weak acid with concentration 0.01 mol/L) is taken, and a 0.01 mol/L lime (base) solution is added. Exactly 25 mL of base is needed for complete neutralisation. If half of that base (12.5 mL) is added, what will the pH be?
  - [Simulation: Acid–base neutralisation and pH change (এসিড–ক্ষার প্রশমন ও pH পরিবর্তন)](https://offschool.site/sim/ssc.chemistry.ch09.titration-ph/): In a school chemistry lab, 25 mL of 0.1 mol/L hydrochloric acid (HCl) is placed in a conical flask with a few drops of phenolphthalein indicator. From a burette, 0.1 mol/L sodium hydroxide (NaOH) solution is added drop by drop. When exactly 25 mL of NaOH has been added, the acid and base completely neutralise each other (equivalence point). What will the pH of the mixture be at this equivalence point?
  - [Simulation: Why won't soap lather in tube-well water? (নলকূপের খর পানিতে সাবানের ফেনা হয় না কেন?)](https://offschool.site/sim/ssc.chemistry.ch09.tubewell-hard-water/): Washing clothes with tube-well water in a village in Rajshahi, Nasrin finds that the soap gives no lather however hard she rubs, and a grey layer floats on the water instead. Her neighbour says water rich in minerals should make soap work even better. What happens when soap solution is added to rain water, and to the hard tube-well water?
- [Chapter 10: Mineral Resources: Metals and Non-metals (খনিজ সম্পদ: ধাতু-অধাতু)](https://offschool.site/subjects/chemistry/ch10/)
  - [Topic: Materials found underground (মাটির নিচে প্রাপ্ত পদার্থসমূহ)](https://offschool.site/subjects/chemistry/ch10/t01/)
  - [Topic: Pictures of different ores (বিভিন্ন আকরিকের চিত্র)](https://offschool.site/subjects/chemistry/ch10/t02/)
  - [Topic: Relation between rocks, minerals and ores (শিলা, খনিজ ও আকরিকের মধ্যে সম্পর্ক)](https://offschool.site/subjects/chemistry/ch10/t03/)
  - [Topic: Ways of extracting metals (ধাতু নিষ্কাশনের উপায়)](https://offschool.site/subjects/chemistry/ch10/t04/)
  - [Topic: Extracting metals according to the reactivity series (electrolysis and carbon reduction) (সক্রিয়তা সিরিজ অনুযায়ী ধাতু নিষ্কাশন (তড়িৎ বিশ্লেষণ ও কার্বন বিজারণ))](https://offschool.site/subjects/chemistry/ch10/t05/)
  - [Topic: Alloys (ধাতুসংকর)](https://offschool.site/subjects/chemistry/ch10/t06/)
  - [Topic: Why alloys (bell metal, brass, steel, coins) and some pure metals are used (সংকর ধাতু (কাঁসা, পিতল, স্টিল, মুদ্রা) ও কিছু বিশুদ্ধ ধাতু ব্যবহারের কারণ)](https://offschool.site/subjects/chemistry/ch10/t07/)
  - [Topic: Corrosion of metals and alloys: symptoms, causes and prevention (ধাতু ও সংকর ধাতুর ক্ষয়: লক্ষণ, কারণ ও প্রতিকার)](https://offschool.site/subjects/chemistry/ch10/t11/)
  - [Topic: Sources, extraction and uses of sulphur and its effect on the environment (সালফারের উৎস, আহরণ ও ব্যবহার এবং পরিবেশের উপর এর প্রভাব)](https://offschool.site/subjects/chemistry/ch10/t08/)
  - [Topic: Recycling of mineral resources (খনিজ উপাদানসমূহের পুনঃব্যবহার)](https://offschool.site/subjects/chemistry/ch10/t09/)
  - [Topic: Finite metal and fossil fuel resources and ways to conserve them (ধাতুসম্পদ ও জীবাশ্ম জ্বালানির সসীমতা ও সংরক্ষণের উপায়)](https://offschool.site/subjects/chemistry/ch10/t10/)
  - [Simulation: Metal extraction: Aluminium vs iron (ধাতু নিষ্কাশন: অ্যালুমিনিয়াম বনাম আয়রন)](https://offschool.site/sim/ssc.chemistry.ch10.aluminium-vs-iron-extraction/): In Bangladeshi steel mills, iron is extracted from its ore by heating with carbon (coke) in a blast furnace. On the other hand, aluminium is widely used in our kitchens for cookware and utensils. In the reactivity series, aluminium sits above zinc and iron. How is aluminium metal extracted from its ore bauxite?
  - [Simulation: Metal reactivity series: Iron nail and copper sulfate (ধাতুর সক্রিয়তা সিরিজ: লোহার পেরেক ও কপার সালফেট)](https://offschool.site/sim/ssc.chemistry.ch10.iron-nail-copper/): In the school chemistry lab, an iron (Fe) nail weighing 5.6 g is placed into a blue copper sulfate (CuSO₄) solution. A reddish copper coating forms on the nail and 6.35 g of copper is displaced (Fe + CuSO₄ → FeSO₄ + Cu). Next, Rafi places a 6.35 g copper (Cu) wire into light green ferrous sulfate (FeSO₄) solution. Between the two mixtures, which combination undergoes a displacement reaction?
  - [Simulation: What does tin do to copper? (তামায় টিন মেশালে কী হয়?)](https://offschool.site/sim/ssc.chemistry.ch10.kasa-bell-metal/): The kasa smiths of Dhamrai melt about 22% tin into copper to make bell-metal plates, bowls and bells. Pure copper is soft and bends easily. What does mixing in tin do to the metal's hardness and melting point?
  - [Simulation: Why doesn't a steel spoon rust? (স্টিলের চামচে মরিচা ধরে না কেন?)](https://offschool.site/sim/ssc.chemistry.ch10.rust-free-spoon/): In the kitchen an iron pan rusts red within days, yet a stainless steel spoon stays shiny for years. Both are mostly iron. What protects the spoon from rust?
  - [Simulation: Why extra air in a sulfuric acid plant? (সালফিউরিক এসিড কারখানায় বাড়তি বাতাস কেন?)](https://offschool.site/sim/ssc.chemistry.ch10.sulfuric-acid-extra-air/): The TSP fertiliser complex in Chattogram makes its own sulfuric acid. Sulfur dioxide from burning sulfur reacts with oxygen from the air over a vanadium(V) oxide catalyst to form sulfur trioxide. Apprentice Sakib notices that far more air goes in than the equation needs. Does the extra oxygen do anything useful?
- [Chapter 11: Mineral Resources: Fossils (খনিজ সম্পদ: জীবাশ্ম)](https://offschool.site/subjects/chemistry/ch11/)
  - [Topic: Components of petroleum (পেট্রোলিয়ামের উপাদানসমূহ)](https://offschool.site/subjects/chemistry/ch11/t01/)
  - [Topic: Uses of petroleum (পেট্রোলিয়ামের ব্যবহার)](https://offschool.site/subjects/chemistry/ch11/t02/)
  - [Topic: Hydrocarbons (হাইড্রোকার্বন)](https://offschool.site/subjects/chemistry/ch11/t03/)
  - [Topic: Aromatic hydrocarbons (অ্যারোমেটিক হাইড্রোকার্বন)](https://offschool.site/subjects/chemistry/ch11/t13/)
  - [Topic: Preparation and properties of saturated and unsaturated hydrocarbons (সম্পৃক্ত ও অসম্পৃক্ত হাইড্রোকার্বনের প্রস্তুতির বিক্রিয়া ও ধর্ম)](https://offschool.site/subjects/chemistry/ch11/t04/)
  - [Topic: Polymers (পলিমার)](https://offschool.site/subjects/chemistry/ch11/t14/)
  - [Topic: Plastics (প্লাস্টিক দ্রব্য)](https://offschool.site/subjects/chemistry/ch11/t05/)
  - [Topic: Effect of plastics on the environment (পরিবেশের উপর প্লাস্টিক দ্রব্যের প্রভাব)](https://offschool.site/subjects/chemistry/ch11/t06/)
  - [Topic: The effect of plastics on the environment in pictures and video (ছবি ও ভিডিওতে পরিবেশের উপর প্লাস্টিক দ্রব্যের প্রভাব)](https://offschool.site/subjects/chemistry/ch11/t07/)
  - [Topic: Proper use of natural gas and petroleum (প্রাকৃতিক গ্যাস ও পেট্রোলিয়ামের যথাযথ ব্যবহার)](https://offschool.site/subjects/chemistry/ch11/t08/)
  - [Topic: Use of hydrocarbons in preparing alcohols, aldehydes and organic acids (অ্যালকোহল, অ্যালডিহাইড ও জৈব এসিডের প্রস্তুতিতে হাইড্রোকার্বনের ব্যবহার)](https://offschool.site/subjects/chemistry/ch11/t10/)
  - [Topic: Investigation into the effect of plastics on the environment (পরিবেশে প্লাস্টিকের প্রভাব নিয়ে অনুসন্ধানমূলক কাজ)](https://offschool.site/subjects/chemistry/ch11/t11/)
  - [Topic: Telling organic from inorganic compounds by experiment (পরীক্ষার মাধ্যমে জৈব ও অজৈব যৌগের পার্থক্যকরণ)](https://offschool.site/subjects/chemistry/ch11/t12/)
  - [Simulation: Telling organic from inorganic by heating (তাপ দিয়ে জৈব আর অজৈব যৌগ চেনা)](https://offschool.site/sim/ssc.chemistry.ch11.char-test-organic/): One test tube holds a little sugar, the other a little table salt. Both are white and grainy and look almost the same. The teacher says strong heating will show which one is an organic compound. Sakib thinks anything heated hard enough turns black. Which one will leave a black residue?
  - [Simulation: Hydrocarbon families: CNG, LPG and ethene (হাইড্রোকার্বনের সমগোত্রীয় শ্রেণি: সিএনজি, এলপিজি ও ইথিন)](https://offschool.site/sim/ssc.chemistry.ch11.cng-lpg-hydrocarbon-families/): In Dhaka, CNG auto-rickshaws run on natural gas whose main component is methane (CH₄, a 1-carbon alkane). Domestic LPG cylinders hold 3- and 4-carbon propane and butane (alkanes). At Karwan Bazar, ethene gas (C₂H₄, a 2-carbon alkene) is used to ripen bananas. Alkenes contain a double bond between two adjacent carbon atoms. Following this pattern, what is the molecular formula of a four-carbon alkene (butene)?
  - [Simulation: How does ethanol become vinegar? (ইথানল থেকে ভিনেগার কীভাবে?)](https://offschool.site/sim/ssc.chemistry.ch11.ethanol-to-vinegar/): Date palm juice left open first smells sweet and sour, then turns sour like vinegar: its sugar becomes ethanol, which oxygen in the air then oxidises to ethanoic acid. In the lab, if ethanol is warmed with excess acidified potassium dichromate, what forms, and what colour change is seen?
  - [Simulation: How heavy is one molecule of PVC pipe? (পিভিসি পাইপের একটি অণু কত ভারী?)](https://offschool.site/sim/ssc.chemistry.ch11.polythene-bag-chain/): A polythene bag is made of thousands of small ethene molecules joined together; 1000 ethene units make a chain of molar mass 28 000 g/mol. The PVC in household water pipes is made by joining vinyl chloride (molar mass 62.5). What is the molar mass of a PVC chain of 2000 units?
  - [Simulation: Fractional distillation of petroleum at Eastern Refinery (ইস্টার্ন রিফাইনারিতে পেট্রোলিয়ামের আংশিক পাতন)](https://offschool.site/sim/ssc.chemistry.ch11.refinery-column/): At Eastern Refinery Limited (ERL) in Patenga, Chattogram, crude petroleum is heated to 400 °C into vapour and fed into a fractional distillation column. The column is hottest near the bottom (350 °C) and gradually cools toward the top (20 °C). As hydrocarbon vapour rises, it condenses into liquid only when the tray temperature drops to or below its boiling point. For example, 12-carbon kerosene (C₁₂H₂₆, boiling point 216 °C) condenses at a lower tray of 200 °C. Octane (C₈H₁₈), the primary component of petrol, has 8 carbon atoms and a boiling point of 126 °C. At which tray in the column will octane vapour condense into liquid?
- [Chapter 12: Chemistry in Our Lives (আমাদের জীবনে রসায়ন)](https://offschool.site/subjects/chemistry/ch12/)
  - [Topic: Sources, properties and uses of some household food items (গৃহে ব্যবহার্য কতিপয় খাদ্য সামগ্রীর আহরণ, ধর্ম ও ব্যবহার)](https://offschool.site/subjects/chemistry/ch12/t01/)
  - [Topic: Importance of pH in judging the suitability of cosmetics (প্রসাধন সামগ্রীর উপযোগিতা নির্ধারণে pH এর গুরুত্ব)](https://offschool.site/subjects/chemistry/ch12/t02/)
  - [Topic: Preparation, properties and cleaning action of household cleaning agents (গৃহে ব্যবহার্য পরিষ্কারক সামগ্রীর প্রস্তুতি, ধর্ম ও পরিষ্কার করার কৌশল)](https://offschool.site/subjects/chemistry/ch12/t03/)
  - [Topic: Availability, properties and uses of compounds used in agriculture (কৃষিক্ষেত্রে ব্যবহৃত উপযুক্ত যৌগের প্রাপ্যতা, ধর্ম ও ব্যবহার)](https://offschool.site/subjects/chemistry/ch12/t04/)
  - [Topic: Harmful effects of chemical wastes (heavy metals, pesticides, industrial dyes, tannery waste, soap, detergent) (রাসায়নিক বর্জ্য (ভারী ধাতু, কীটনাশক, শিল্প রং, ট্যানারি বর্জ্য, সাবান, ডিটারজেন্ট) এর ক্ষতিকর প্রভাব)](https://offschool.site/subjects/chemistry/ch12/t05/)
  - [Topic: Making soap (সাবান প্রস্তুতি)](https://offschool.site/subjects/chemistry/ch12/t06/)
  - [Topic: Proper use of chemicals to prevent soil, water and air pollution (মাটি, পানি ও বায়ু দূষণ রোধে রাসায়নিক দ্রব্যের যথাযথ ব্যবহার)](https://offschool.site/subjects/chemistry/ch12/t07/)
  - [Topic: Demonstrating the bleaching action of bleaching powder (ব্লিচিং পাউডারের বিরঞ্জন ক্রিয়া প্রদর্শন)](https://offschool.site/subjects/chemistry/ch12/t08/)
  - [Topic: Experiment on the role of baking powder in food (খাদ্য দ্রব্যে বেকিং পাউডারের ভূমিকা পরীক্ষা)](https://offschool.site/subjects/chemistry/ch12/t09/)
  - [Simulation: Decomposition and balancing of baking soda in the kitchen (রান্নাঘরে খাবার সোডার বিয়োজন ও সমতাকরণ)](https://offschool.site/sim/ssc.chemistry.ch12.baking-soda-pitha/): When making steamed pitha or cake at home, a little baking soda (NaHCO₃) is mixed into the batter and heated. On heating, baking soda decomposes into sodium carbonate (Na₂CO₃), water (H₂O), and carbon dioxide (CO₂) gas. The bubbles of CO₂ gas make the pitha rise and become fluffy and soft. In a chemical reaction, atoms cannot be created or destroyed. To conserve all atoms of every element on both sides, what are the correct coefficients for NaHCO₃, Na₂CO₃, H₂O, and CO₂?
  - [Simulation: Why does bleaching powder turn dyed cloth white? (ব্লিচিং পাউডারে রঙিন কাপড় সাদা হয় কেন?)](https://offschool.site/sim/ssc.chemistry.ch12.bleaching-powder-cloth/): At the laundry, Hasan sees that a white shirt with a dye stain loses the stain when soaked in water with bleaching powder. He thinks the water must wash the dye out, so the water should turn red. What happens to a piece of red-dyed cotton cloth left with bleaching powder?
  - [Simulation: How soap cleans dirt and oil (সাবান কীভাবে ময়লা ও তেল পরিষ্কার করে?)](https://offschool.site/sim/ssc.chemistry.ch12.how-soap-cleans/): During lunch, Sadaf got an oily curry stain on his white cotton shirt. He rubbed it with tube-well water for 5 minutes, but the non-polar oil stain did not come out at all. Yet when he applied a little soap and rinsed with water, the stain washed away easily. Given that water molecules are polar, why does water alone fail to remove non-polar oil stains from cloth?
  - [Simulation: Lime kiln: quicklime from limestone (চুনের ভাটি: চুনাপাথর থেকে কুইকলাইম)](https://offschool.site/sim/ssc.chemistry.ch12.lime-kiln-quicklime/): Quicklime (CaO) for paan and for reducing soil acidity is made by heating limestone or shells in a kiln: CaCO₃ → CaO + CO₂. Heating 50 g of limestone leaves 28 g of solid quicklime, while 22 g of carbon dioxide (CO₂) gas escapes into the air. If 100 g of limestone is heated in the kiln, what mass of quicklime will remain?
  - [Simulation: Making soap from soybean oil (সয়াবিন তেল থেকে সাবান তৈরি)](https://offschool.site/sim/ssc.chemistry.ch12.soap-from-soybean-oil/): In a small soap factory in Narayanganj, oil and caustic soda solution are mixed in a big pan and boiled for hours. Shawon wonders why all the boiling is needed; mixing oil and soda should make soap straight away. In a test tube of soybean oil with caustic soda, what happens without heat and with heat?

## Biology (জীববিজ্ঞান)

Cells and cell division, bioenergetics, digestion, transport, respiration, excretion, coordination, reproduction, heredity, ecology and biotechnology, life's processes step by step.

- [SSC Biology](https://offschool.site/subjects/biology/): কোষ ও কোষ বিভাজন, জীবনীশক্তি, পরিপাক, পরিবহণ, শ্বসন, রেচন, সমন্বয়, প্রজনন, বংশগতি, পরিবেশ ও জীবপ্রযুক্তি, জীবনের প্রক্রিয়াগুলো ধাপে ধাপে।
- [Chapter 1: Lessons on Life (জীবনপাঠ)](https://offschool.site/subjects/biology/ch01/)
  - [Topic: Concept of Biology (জীববিজ্ঞানের ধারণা)](https://offschool.site/subjects/biology/ch01/t01/)
  - [Topic: Introduction to the Branches of Biology (জীববিজ্ঞানের শাখাসমূহের পরিচিতি)](https://offschool.site/subjects/biology/ch01/t02/)
  - [Topic: Classification of organisms (জীবের শ্রেণিবিন্যাস)](https://offschool.site/subjects/biology/ch01/t03/)
  - [Topic: Concept of classification (শ্রেণিবিন্যাসের ধারণা)](https://offschool.site/subjects/biology/ch01/t04/)
  - [Topic: Classification System of Organisms (জীবের শ্রেণিবিন্যাসকরণ পদ্ধতি)](https://offschool.site/subjects/biology/ch01/t05/)
  - [Topic: Binomial Nomenclature (দ্বিপদ নামকরণ)](https://offschool.site/subjects/biology/ch01/t06/)
  - [Topic: Concept of binomial nomenclature (দ্বিপদ নামকরণের ধারণা)](https://offschool.site/subjects/biology/ch01/t07/)
  - [Topic: Importance of binomial nomenclature (দ্বিপদ নামকরণের গুরুত্ব)](https://offschool.site/subjects/biology/ch01/t08/)
  - [Simulation: Which two organisms are more closely related? (কোন দুটি জীব বেশি নিকটাত্মীয়?)](https://offschool.site/sim/ssc.biology.ch01.classify-organisms/): In Linnaean taxonomy, organisms are classified into 7 major hierarchical ranks: Kingdom, Phylum, Class, Order, Family, Genus, and Species. Rohu fish (Labeo rohita) and Hilsa fish (Tenualosa ilisha) share the first 3 ranks (Kingdom, Phylum, and Class). In contrast, the fierce Royal Bengal tiger (Panthera tigris) in the Sundarbans and the gentle domestic cat (Felis catus) at home differ vastly in size and lifestyle. How many of the 7 taxonomic ranks do the tiger and cat share?
- [Chapter 2: Cells and Tissues of Organisms (জীবকোষ ও টিস্যু)](https://offschool.site/subjects/biology/ch02/)
  - [Topic: Functions of the main organelles of plant and animal cells (following their electron microscopic structure) (উদ্ভিদ ও প্রাণিকোষের প্রধান অঙ্গাণুর কাজ (ইলেকট্রন মাইক্রোস্কোপিক গঠন অনুসরণে))](https://offschool.site/subjects/biology/ch02/t01/)
  - [Topic: Role of different types of cells in the functioning of nerves, muscles, blood, skin and bones in the human body (মানবদেহের স্নায়ু, পেশি, রক্ত, ত্বক এবং অস্থির কাজ পরিচালনায় বিভিন্ন প্রকার কোষের ভূমিকা)](https://offschool.site/subjects/biology/ch02/t02/)
  - [Topic: Plant tissues (উদ্ভিদ টিস্যু)](https://offschool.site/subjects/biology/ch02/t03/)
  - [Topic: Simple tissues (parenchyma, collenchyma, sclerenchyma) (সরল টিস্যু (প্যারেনকাইমা, কোলেনকাইমা, স্ক্লেরেনকাইমা))](https://offschool.site/subjects/biology/ch02/t04/)
  - [Topic: Complex tissues (xylem and phloem) (জটিল টিস্যু (জাইলেম ও ফ্লোয়েম))](https://offschool.site/subjects/biology/ch02/t05/)
  - [Topic: Animal tissues and their functions (প্রাণিটিস্যু ও এর কাজ)](https://offschool.site/subjects/biology/ch02/t06/)
  - [Topic: Epithelial tissue (আবরণী টিস্যু)](https://offschool.site/subjects/biology/ch02/t07/)
  - [Topic: Connective tissue (যোজক টিস্যু)](https://offschool.site/subjects/biology/ch02/t08/)
  - [Topic: Muscle tissue (পেশি টিস্যু)](https://offschool.site/subjects/biology/ch02/t09/)
  - [Topic: Nervous tissue (স্নায়ু টিস্যু)](https://offschool.site/subjects/biology/ch02/t10/)
  - [Topic: Organisation of cells into tissues, organs and systems (টিস্যু, অঙ্গ এবং তন্ত্রে কোষের সংগঠন)](https://offschool.site/subjects/biology/ch02/t11/)
  - [Topic: Tissue systems and their functions (টিস্যুতন্ত্র এবং এর কাজ)](https://offschool.site/subjects/biology/ch02/t12/)
  - [Topic: Concept and importance of organs and organ systems (অঙ্গ ও অঙ্গতন্ত্রের ধারণা এবং গুরুত্ব)](https://offschool.site/subjects/biology/ch02/t13/)
  - [Topic: Microscope (অণুবীক্ষণ যন্ত্র)](https://offschool.site/subjects/biology/ch02/t14/)
  - [Simulation: Are runny blood and hard bone the same kind of tissue? (তরল রক্ত আর শক্ত অস্থি কি একই ধরনের টিস্যু?)](https://offschool.site/sim/ssc.biology.ch02.blood-and-bone-tissue/): In biology class the teacher says animal tissues are of four kinds. Rafi argues that blood is a liquid and bone is as hard as stone, so they can never be the same kind of tissue; blood isn't really a tissue at all. Look at the slides under the microscope: what kind of tissue are blood and bone?
  - [Simulation: Why cells are small: Surface area vs. volume (কোষ কেন ক্ষুদ্রাকার: ক্ষেত্রফল বনাম আয়তন)](https://offschool.site/sim/ssc.biology.ch02.cell-size-limit/): A cubic living cell has an edge length of 1 cm, total surface area of 6 cm², volume of 1 cm³, and a surface area to volume ratio (SA:V) of 6 /cm. The cell absorbs nutrients, grows, and its edge length doubles to 2 cm. What will its new surface area to volume ratio (SA:V) be?
  - [Simulation: Which tissue is jute fibre, and which way does water rise? (পাটের আঁশ কোন টিস্যু, আর পানি ওঠে কোন পথে?)](https://offschool.site/sim/ssc.biology.ch02.jute-stem-tissues/): Jute is called the golden fibre of Bangladesh. Jute stems are retted to free long, strong fibres. Rony thinks the fibres must be the pipes that carry water from the roots to the leaves. Look at a stem cross-section under the microscope: which tissue is the strong fibre, and which tissue carries water up?
  - [Simulation: Why can't you see ribosomes even at 1000×? (১০০০ গুণ বড় করলেও রাইবোসোম দেখা যায় না কেন?)](https://offschool.site/sim/ssc.biology.ch02.ribosomes-under-the-microscope/): In the school lab Mitu sees onion peel cells laid out like bricks and cheek cells as flat blue patches. The diagram in her book shows mitochondria, ribosomes and Golgi bodies inside every cell. She will fit the oil-immersion lens and look for ribosomes at 1000×. Will she see them?
- [Chapter 3: Cell Division (কোষ বিভাজন)](https://offschool.site/subjects/biology/ch03/)
  - [Topic: Cell Division (কোষ বিভাজন)](https://offschool.site/subjects/biology/ch03/t01/)
  - [Topic: Concept of cell division (কোষ বিভাজনের ধারণা)](https://offschool.site/subjects/biology/ch03/t02/)
  - [Topic: Types of cell division (কোষ বিভাজনের প্রকারভেদ)](https://offschool.site/subjects/biology/ch03/t03/)
  - [Topic: Mitosis (মাইটোসিস)](https://offschool.site/subjects/biology/ch03/t04/)
  - [Topic: Concept of mitosis (মাইটোসিসের ধারণা)](https://offschool.site/subjects/biology/ch03/t05/)
  - [Topic: Stages of mitosis (মাইটোসিসের পর্যায়)](https://offschool.site/subjects/biology/ch03/t06/)
  - [Topic: Importance of mitosis (মাইটোসিসের গুরুত্ব)](https://offschool.site/subjects/biology/ch03/t07/)
  - [Topic: Meiosis (মিয়োসিস)](https://offschool.site/subjects/biology/ch03/t08/)
  - [Topic: Concept of meiosis (মিয়োসিসের ধারণা)](https://offschool.site/subjects/biology/ch03/t09/)
  - [Topic: Significance of meiosis (মিয়োসিসের তাৎপর্য)](https://offschool.site/subjects/biology/ch03/t10/)
  - [Simulation: Cell division: Onion root tip mitosis vs meiosis (কোষ বিভাজন: পেঁয়াজের মূলের মাইটোসিস বনাম মিয়োসিস)](https://offschool.site/sim/ssc.biology.ch03.mitosis-steps/): In a class nine biology lab, students observed onion (Allium cepa) root tip meristem under a microscope and found 16 chromosomes (2n = 16) in somatic cells dividing by mitosis for root growth. The teacher explained that reproductive mother cells also start with 16 chromosomes, but undergo meiosis to produce pollen and ovules. When an onion reproductive mother cell completes meiosis, how many chromosomes will each daughter gamete cell contain?
- [Chapter 4: Bioenergetics (জীবনীশক্তি)](https://offschool.site/subjects/biology/ch04/)
  - [Topic: Bioenergetics and the Role of ATP (জীবনীশক্তি (Bioenergetics) ও এটিপির ভূমিকা)](https://offschool.site/subjects/biology/ch04/t01/)
  - [Topic: Photosynthesis (সালোকসংশ্লেষণ)](https://offschool.site/subjects/biology/ch04/t02/)
  - [Topic: The process of photosynthesis (সালোকসংশ্লেষণ প্রক্রিয়া)](https://offschool.site/subjects/biology/ch04/t03/)
  - [Topic: Role of chlorophyll and light in photosynthesis (সালোকসংশ্লেষণে ক্লোরোফিল ও আলোর ভূমিকা)](https://offschool.site/subjects/biology/ch04/t04/)
  - [Topic: Role of other factors in photosynthesis (সালোকসংশ্লেষণে অন্যান্য প্রভাবকের ভূমিকা)](https://offschool.site/subjects/biology/ch04/t05/)
  - [Topic: Importance of photosynthesis (সালোকসংশ্লেষণের গুরুত্ব)](https://offschool.site/subjects/biology/ch04/t06/)
  - [Topic: Respiration (শ্বসন)](https://offschool.site/subjects/biology/ch04/t07/)
  - [Topic: Aerobic and Anaerobic Respiration (সবাত ও অবাত শ্বসন)](https://offschool.site/subjects/biology/ch04/t08/)
  - [Topic: Importance of respiration (শ্বসনের গুরুত্ব)](https://offschool.site/subjects/biology/ch04/t09/)
  - [Simulation: Photosynthesis rate and limiting factors (সালোকসংশ্লেষণের হার ও সীমাবদ্ধতাকারী প্রভাবক)](https://offschool.site/sim/ssc.biology.ch04.photosynthesis-limits/): In a biology lab experiment, a Hydrilla twig is placed in water to observe photosynthesis at 30 °C with dissolved CO₂ at 500 ppm. At 20% light intensity, 20 oxygen bubbles emerge per minute. If the light intensity is increased to 60% (three times), how many bubbles will emerge per minute?
  - [Simulation: Sprint race, anaerobic respiration and ATP: Muscle fatigue (স্প্রিন্ট দৌড়, অবাত শ্বসন ও এটিপি: পেশি ক্লান্তি)](https://offschool.site/sim/ssc.biology.ch04.sprint-respiration-atp/): Class nine student Rimi competed in the 100-metre sprint on annual sports day. Right after crossing the finish line in first place, she experienced severe pain and cramps in her leg muscles and began panting heavily. Normally, with ample oxygen, complete aerobic respiration of 1 molecule of glucose yields 38 ATP. But during a sprint, muscle cells suffer acute oxygen deficiency and temporarily switch to anaerobic respiration (lactic acid fermentation). In this oxygen deficit, how many ATP molecules in total does 1 molecule of glucose produce in Rimi's muscle cells?
  - [Simulation: Where does oxygen come from in photosynthesis? (সালোকসংশ্লেষণে অক্সিজেন কোথা থেকে আসে?)](https://offschool.site/sim/ssc.biology.ch04.where-oxygen-comes-from/): In a class nine biology lab, students observe bubbles of gas steadily rising from a submerged Hydrilla twig placed by a sunny window. The plant takes up carbon dioxide (CO₂) and water (H₂O) to carry out photosynthesis in sunlight, synthesizing glucose in its leaves. The released gas is confirmed to be oxygen. But where does this released oxygen actually come from: does it originate from carbon dioxide, or from water?
- [Chapter 5: Food, Nutrition and Digestion (খাদ্য, পুষ্টি এবং পরিপাক)](https://offschool.site/subjects/biology/ch05/)
  - [Topic: Nutrition of plants (উদ্ভিদের পুষ্টি)](https://offschool.site/subjects/biology/ch05/t01/)
  - [Topic: Nutrition and its essential elements (পুষ্টি ও তার প্রয়োজনীয় উপাদান)](https://offschool.site/subjects/biology/ch05/t02/)
  - [Topic: Deficiency symptoms of nutrients (পুষ্টির অভাবজনিত লক্ষণসমূহ)](https://offschool.site/subjects/biology/ch05/t03/)
  - [Topic: Food and nutrition of animals (প্রাণীর খাদ্য ও পুষ্টি)](https://offschool.site/subjects/biology/ch05/t04/)
  - [Topic: Main components of food and their sources (খাদ্যের প্রধান উপাদান ও উৎস)](https://offschool.site/subjects/biology/ch05/t05/)
  - [Topic: Ideal food pyramid (আদর্শ খাদ্য পিরামিড)](https://offschool.site/subjects/biology/ch05/t06/)
  - [Topic: Principles of healthy eating (খাদ্য গ্রহণের নিয়মনীতি (Healthy eating))](https://offschool.site/subjects/biology/ch05/t07/)
  - [Topic: Nutritional deficiency diseases (পুষ্টির অভাবজনিত রোগ)](https://offschool.site/subjects/biology/ch05/t08/)
  - [Topic: Goitre (গলগণ্ড)](https://offschool.site/subjects/biology/ch05/t09/)
  - [Topic: Night blindness (রাতকানা)](https://offschool.site/subjects/biology/ch05/t10/)
  - [Topic: Rickets (রিকেট)](https://offschool.site/subjects/biology/ch05/t11/)
  - [Topic: Anaemia (রক্তশূন্যতা)](https://offschool.site/subjects/biology/ch05/t12/)
  - [Topic: Energy in nutrients (পুষ্টি উপাদানে শক্তি (Energy in nutrients))](https://offschool.site/subjects/biology/ch05/t13/)
  - [Topic: Amount of energy per kilogram of nutrient (প্রতি কেজি পুষ্টি উপাদানে শক্তির পরিমাণ)](https://offschool.site/subjects/biology/ch05/t14/)
  - [Topic: Energy used in activities (in kilocalories and kilojoules) (ক্রিয়াকর্মে ব্যয়িত শক্তি (কিলোক্যালরি ও কিলোজুলে))](https://offschool.site/subjects/biology/ch05/t15/)
  - [Topic: BMI and BMR (বিএমআই (BMI) এবং বিএমআর (BMR))](https://offschool.site/subjects/biology/ch05/t16/)
  - [Topic: Importance of BMI and BMR (বিএমআই ও বিএমআর-এর গুরুত্ব)](https://offschool.site/subjects/biology/ch05/t17/)
  - [Topic: Calculating BMI and BMR (বিএমআই ও বিএমআর হিসাব)](https://offschool.site/subjects/biology/ch05/t18/)
  - [Topic: Relationship between BMR and energy expended (বি এম আর এবং ব্যয়িত শক্তির সম্পর্ক)](https://offschool.site/subjects/biology/ch05/t19/)
  - [Topic: BMI (age and sex) (বিএমআই (বয়স ও লিঙ্গ))](https://offschool.site/subjects/biology/ch05/t20/)
  - [Topic: Importance of exercise and rest (শরীরচর্চা এবং বিশ্রামের গুরুত্ব)](https://offschool.site/subjects/biology/ch05/t21/)
  - [Topic: Use of chemicals in food preservation and their effects on the body (খাদ্যদ্রব্য সংরক্ষণে রাসায়নিক পদার্থের ব্যবহার ও এর শারীরিক প্রতিক্রিয়া)](https://offschool.site/subjects/biology/ch05/t22/)
  - [Topic: Use of colouring agents in food (খাদ্যে রঞ্জক ব্যবহার)](https://offschool.site/subjects/biology/ch05/t23/)
  - [Topic: Main parts and accessory organs of the human digestive system and their functions (মানুষের পৌষ্টিকতন্ত্রের প্রধান অংশ ও সহায়তাকারী অঙ্গ এবং এর কাজ)](https://offschool.site/subjects/biology/ch05/t24/)
  - [Topic: Ingestion (গলাধঃকরণ)](https://offschool.site/subjects/biology/ch05/t25/)
  - [Topic: Digestion of food (খাদ্য পরিপাক)](https://offschool.site/subjects/biology/ch05/t26/)
  - [Topic: Absorption (শোষণ)](https://offschool.site/subjects/biology/ch05/t27/)
  - [Topic: Assimilation (আত্তীকরণ)](https://offschool.site/subjects/biology/ch05/t28/)
  - [Topic: Egestion (নিঃসরণ)](https://offschool.site/subjects/biology/ch05/t29/)
  - [Topic: Functions of the liver (যকৃতের (Liver) কাজ)](https://offschool.site/subjects/biology/ch05/t30/)
  - [Topic: Role of the liver in digestion (পরিপাকে যকৃতের ভূমিকা)](https://offschool.site/subjects/biology/ch05/t31/)
  - [Topic: Metabolism of glucose and amino acids (গ্লুকোজ এবং অ্যামাইনো এসিডের বিপাক)](https://offschool.site/subjects/biology/ch05/t32/)
  - [Topic: Production of urea (ইউরিয়া উৎপাদন)](https://offschool.site/subjects/biology/ch05/t33/)
  - [Topic: Functions of the pancreas (অগ্ন্যাশয়ের (Pancreas) কাজ)](https://offschool.site/subjects/biology/ch05/t34/)
  - [Topic: Intestinal problems (আন্ত্রিক সমস্যা)](https://offschool.site/subjects/biology/ch05/t35/)
  - [Topic: Indigestion (অজীর্ণতা)](https://offschool.site/subjects/biology/ch05/t36/)
  - [Topic: Dysentery (আমাশয়)](https://offschool.site/subjects/biology/ch05/t37/)
  - [Topic: Constipation (কোষ্ঠকাঠিন্য)](https://offschool.site/subjects/biology/ch05/t38/)
  - [Topic: Gastric ulcer (গ্যাস্ট্রিক আলসার)](https://offschool.site/subjects/biology/ch05/t39/)
  - [Topic: Appendicitis (অ্যাপেনডিসাইটিস)](https://offschool.site/subjects/biology/ch05/t40/)
  - [Topic: Worm diseases (কৃমিজনিত রোগ)](https://offschool.site/subjects/biology/ch05/t41/)
  - [Topic: Diarrhoea (ডায়ারিয়া)](https://offschool.site/subjects/biology/ch05/t42/)
  - [Simulation: Same BMI, different ages: is Nabila underweight? (একই বিএমআই, ভিন্ন বয়স: নাবিলা কি কম ওজনের?)](https://offschool.site/sim/ssc.biology.ch05.bmi-check-teen/): Nabila, aged 15, is 155 cm tall and weighs 40 kg. Her 25-year-old cousin has exactly the same height and mass. An online calculator gives both a BMI of 16.6 and says 'underweight'. Nabila's mother is worried. Is the same verdict right for both of them?
  - [Simulation: How long must you walk to use up one singara? (একটা সিঙ্গারার শক্তি খরচ করতে কতক্ষণ হাঁটতে হবে?)](https://offschool.site/sim/ssc.biology.ch05.burn-a-singara/): At tiffin Tanvir eats two singaras, each about 260 kilocalories. He says a ten-minute walk home from school uses all that energy up. Tanvir's mass is 45 kg. How long must he really walk to use up one singara's energy?
  - [Simulation: Digestion journey of rice, dal, and fish (ভাত, ডাল ও মাছের পরিপাক যাত্রা)](https://offschool.site/sim/ssc.biology.ch05.digestion-journey/): Ratul, a class nine student, ate a lunch of hot rice, lentil soup (dal), and fried rui fish. Rice is carbohydrate (starch), dal is plant protein, and fish is animal protein. As he chews the food in his mouth, salivary ptyalin begins breaking down the boiled starch in the rice into maltose. In which organ of the human digestive tract does the chemical digestion of the protein from dal and fish actually begin?
  - [Simulation: Hilsa fat and bile emulsification (ইলিশের চর্বি ও পিত্তরসের ইমালসিফিকেশন)](https://offschool.site/sim/ssc.biology.ch05.hilsa-bile-emulsion/): After eating fried hilsa for lunch, a large drop of fat reaches the digestive tract. Model this fat drop as a cube with edge length 6 cm and surface area 216 cm². Bile from the liver emulsifies this drop, splitting it into 10 pieces along each edge to create 1,000 identical tiny droplets. What will be the combined total surface area of all these droplets?
  - [Simulation: 10 g of oil or 10 g of sugar: which has more energy? (১০ গ্রাম তেল না ১০ গ্রাম চিনি: কোনটিতে শক্তি বেশি?)](https://offschool.site/sim/ssc.biology.ch05.oil-vs-sugar-energy/): The sweet-shop owner says sugar gives the most energy of all, so eat sweets before an exam. Nipa thinks cooking oil has energy too. For the same mass, 10 g of oil or 10 g of sugar, which gives more energy?
  - [Simulation: Is Rafi's dinner balanced? (রাফির রাতের খাবার কি সুষম?)](https://offschool.site/sim/ssc.biology.ch05.rafi-dinner-plate/): The night before an exam, Rafi has two plates of rice, two singaras and a bottle of soft drink for dinner. He says he is full and has plenty of energy, so the meal must be nutritious. His mother says a meal without dal, fish and greens isn't balanced. What is actually too little and too much in Rafi's meal?
  - [Simulation: Why are the lower rice leaves yellow? (ধানের নিচের পাতা হলুদ কেন?)](https://offschool.site/sim/ssc.biology.ch05.rice-leaves-turn-yellow/): A farmer in Bogura notices the old lower leaves of his rice turning yellow while the young upper leaves stay green. The agriculture officer says one nutrient is short. In class you grow seedlings in culture solutions, each missing one element. Without nitrogen, which leaves turn yellow first?
- [Chapter 6: Transport in Organisms (জীবে পরিবহণ)](https://offschool.site/subjects/biology/ch06/)
  - [Topic: Transport in Plants (উদ্ভিদে পরিবহণ)](https://offschool.site/subjects/biology/ch06/t01/)
  - [Topic: Concept of transport in plants (উদ্ভিদে পরিবহণের ধারণা)](https://offschool.site/subjects/biology/ch06/t02/)
  - [Topic: Need for transport in plants (উদ্ভিদে পরিবহণের প্রয়োজনীয়তা)](https://offschool.site/subjects/biology/ch06/t03/)
  - [Topic: Plant and Water Relationship (উদ্ভিদ ও পানির সম্পর্ক)](https://offschool.site/subjects/biology/ch06/t04/)
  - [Topic: Imbibition (ইমবাইবিশন)](https://offschool.site/subjects/biology/ch06/t05/)
  - [Topic: Diffusion (ব্যাপন)](https://offschool.site/subjects/biology/ch06/t06/)
  - [Topic: Osmosis (অভিস্রবণ)](https://offschool.site/subjects/biology/ch06/t07/)
  - [Topic: Absorption of Water and Mineral Salts (পানি ও খনিজ পদার্থের শোষণ)](https://offschool.site/subjects/biology/ch06/t08/)
  - [Topic: Translocation of Substances Produced in Photosynthesis (সালোক সংশ্লেষণে উৎপাদিত পদার্থের পরিবহণ)](https://offschool.site/subjects/biology/ch06/t09/)
  - [Topic: Conduction of Water and Mineral Salts (পানি ও খনিজ পদার্থের পরিবহণ)](https://offschool.site/subjects/biology/ch06/t10/)
  - [Topic: Transpiration (প্রস্বেদন)](https://offschool.site/subjects/biology/ch06/t11/)
  - [Topic: Concept and significance of transpiration (প্রস্বেদনের ধারণা ও তাৎপর্য)](https://offschool.site/subjects/biology/ch06/t12/)
  - [Topic: Factors affecting transpiration: temperature, air and humidity (প্রস্বেদনের প্রভাবক: তাপমাত্রা, বায়ু ও আর্দ্রতা)](https://offschool.site/subjects/biology/ch06/t13/)
  - [Topic: Circulation in the Human Body (মানবদেহে সংবহন)](https://offschool.site/subjects/biology/ch06/t14/)
  - [Topic: Components and Functions of Blood (রক্তের উপাদান ও কাজ)](https://offschool.site/subjects/biology/ch06/t15/)
  - [Topic: Characteristics of Blood Groups and Blood Selection (রক্ত গ্রুপের বৈশিষ্ট্য ও রক্ত নির্বাচন)](https://offschool.site/subjects/biology/ch06/t16/)
  - [Topic: Blood Donation and Social Commitment (রক্ত দান এবং সামাজিক দায়বদ্ধতা)](https://offschool.site/subjects/biology/ch06/t17/)
  - [Topic: Blood Circulation (রক্ত সঞ্চালন)](https://offschool.site/subjects/biology/ch06/t18/)
  - [Topic: Structure and Function of the Heart (হৃৎপিণ্ডের গঠন ও কাজ)](https://offschool.site/subjects/biology/ch06/t19/)
  - [Topic: Functions of Arteries and Veins (শিরা ও ধমনির কাজ)](https://offschool.site/subjects/biology/ch06/t20/)
  - [Topic: Role of blood pressure (রক্তচাপের ভূমিকা)](https://offschool.site/subjects/biology/ch06/t21/)
  - [Topic: Ideal Blood Pressure (আদর্শ রক্তচাপ)](https://offschool.site/subjects/biology/ch06/t22/)
  - [Topic: Blood Pressure, Pulse Rate and Their Measurement (রক্তচাপ ও পালসরেট এবং এদের পরিমাপ)](https://offschool.site/subjects/biology/ch06/t23/)
  - [Topic: Cholesterol (কোলেস্টেরল)](https://offschool.site/subjects/biology/ch06/t24/)
  - [Topic: Types of cholesterol (কোলেস্টেরলের প্রকারভেদ)](https://offschool.site/subjects/biology/ch06/t25/)
  - [Topic: Normal cholesterol levels in blood (রক্তে কোলেস্টেরলের স্বাভাবিক মাত্রা)](https://offschool.site/subjects/biology/ch06/t26/)
  - [Topic: Benefits and health risks of cholesterol (কোলেস্টেরলের উপকারিতা ও স্বাস্থ্য ঝুঁকি)](https://offschool.site/subjects/biology/ch06/t27/)
  - [Topic: Irregularities in Blood (রক্তের অস্বাভাবিকতা)](https://offschool.site/subjects/biology/ch06/t28/)
  - [Topic: Leukaemia (লিউকেমিয়া)](https://offschool.site/subjects/biology/ch06/t29/)
  - [Topic: Diseases Related to the Heart (হৃৎপিণ্ড সম্পর্কিত রোগ)](https://offschool.site/subjects/biology/ch06/t30/)
  - [Topic: High and Low Blood Pressure (উচ্চ ও নিম্ন রক্তচাপ)](https://offschool.site/subjects/biology/ch06/t31/)
  - [Topic: Rheumatic Fever (বাতজ্বর)](https://offschool.site/subjects/biology/ch06/t32/)
  - [Topic: Heart attack (হার্ট অ্যাটাক)](https://offschool.site/subjects/biology/ch06/t33/)
  - [Topic: Ways to keep the heart healthy (হৃৎপিণ্ডকে সুস্থ রাখার উপায়)](https://offschool.site/subjects/biology/ch06/t34/)
  - [Topic: Choosing the right food for a healthy heart (হৃৎপিণ্ড সুস্থ রাখতে সঠিক খাদ্য নির্বাচন)](https://offschool.site/subjects/biology/ch06/t35/)
  - [Topic: A healthy lifestyle for a healthy heart (হৃৎপিণ্ড সুস্থ রাখতে সঠিক জীবনধারা)](https://offschool.site/subjects/biology/ch06/t36/)
  - [Simulation: Will the dye climb faster without leaves? (পাতা ছিঁড়ে ফেললে রং কি দ্রুত উঠবে?)](https://offschool.site/sim/ssc.biology.ch06.balsam-in-red-ink/): Florists in Shahbag colour white tuberoses by standing their stems in coloured water. In class, Mitu stands a balsam shoot in water with red ink. Her friend says that if all the leaves are pulled off, the water won't have to fill them, so the dye will climb even faster. Is he right?
  - [Simulation: Can the son give blood to his mother? (ছেলে কি মাকে রক্ত দিতে পারবে?)](https://offschool.site/sim/ssc.biology.ch06.blood-for-the-patient/): After surgery at Dhaka Medical College Hospital, Rafi's mother needs blood. Her group is B positive. Rafi is AB positive and assumes a son's blood must suit his mother. Can Rafi give blood to his mother?
  - [Simulation: Where is the needle at the first tap? (প্রথম টক শব্দে কাঁটা কোথায়?)](https://offschool.site/sim/ssc.biology.ch06.blood-pressure-cuff/): At a school health check, the nurse wraps a cuff round Sakib's arm, pumps it to 160 mmHg, then lets the air out slowly while listening with a stethoscope. At some point a tapping starts, and later it stops. What is the reading at the moment the first tap is heard called?
  - [Simulation: Which cells fill a blood smear? (রক্তের স্মিয়ারে কোন কণিকা সবচেয়ে বেশি?)](https://offschool.site/sim/ssc.biology.ch06.blood-smear-cells/): Sumi's blood test report says: per microlitre, 4.8 million red cells, 7 thousand white cells and 250 thousand platelets. Sumi thinks white cells are bigger, so they'll be what she mostly sees. What will a blood smear look like at 400×?
  - [Simulation: Cholesterol in Arteries and Blood Flow (ধমনিতে কোলেস্টেরল ও রক্তপ্রবাহ)](https://offschool.site/sim/ssc.biology.ch06.clogged-artery-flow/): In a healthy person with normal blood pressure of 100 mmHg, blood flow to the leg is 16 mL/s. If cholesterol plaque narrows the leg artery radius by half (to 50%), what will the blood flow drop to at the same blood pressure?
  - [Simulation: Potato in Salt Water: Osmosis (লবণ পানিতে আলুর সংকোচন: অভিস্রবণ)](https://offschool.site/sim/ssc.biology.ch06.potato-osmosis/): When salt is sprinkled on fresh potato slices or when they are placed in salt water, water soon oozes out and the crisp slices become limp and soft. The internal cell sap of a fresh potato (plant cell) has a solute concentration of 0.3 mol/L. If the potato is placed in a 1.2 mol/L salt solution, in which direction will the net movement of water occur across the selectively permeable cell membrane?
  - [Simulation: Will a ringed branch dry up? (বাকল তুলে ফেললে ডাল কি শুকিয়ে যাবে?)](https://offschool.site/sim/ssc.biology.ch06.ringed-mango-branch/): A mango farmer in Rajshahi peels a ring of bark all the way round one branch. A neighbour says water travels in the bark, so the branch will dry up by tomorrow. What will the branch look like a few weeks later?
  - [Simulation: Why did rice wilt in wet soil? (ভেজা মাটিতেও ধানচারা নেতিয়ে পড়ল কেন?)](https://offschool.site/sim/ssc.biology.ch06.salty-soil-rice/): A cyclone surge floods a rice field in Satkhira with salty seawater. The soil is wet, yet two days later the seedlings are wilting as if they had no water. With so much water in the soil, why can't the plants get it?
  - [Simulation: Why do gourd leaves wilt at midday? (দুপুরে লাউয়ের পাতা নেতিয়ে পড়ে কেন?)](https://offschool.site/sim/ssc.biology.ch06.wilting-gourd-leaves/): On a hot, windy afternoon the leaves of a gourd vine on its trellis droop, yet by evening they are fresh again. Raju thinks plants only take in water through their roots and never lose any through their leaves. Do leaves lose water, and when do they lose the most?
- [Chapter 7: Exchange of Gases (গ্যাসীয় বিনিময়)](https://offschool.site/subjects/biology/ch07/)
  - [Topic: Gaseous Exchange in Plants (উদ্ভিদে গ্যাসীয় বিনিময়)](https://offschool.site/subjects/biology/ch07/t01/)
  - [Topic: Main Parts of Human Respiratory System (মানব শ্বসনতন্ত্রের প্রধান অংশসমূহ)](https://offschool.site/subjects/biology/ch07/t02/)
  - [Topic: Structure of the Lungs (ফুসফুসের গঠন)](https://offschool.site/subjects/biology/ch07/t03/)
  - [Topic: Breathing Process and Gaseous Exchange (শ্বাস-প্রশ্বাস প্রক্রিয়া ও গ্যাসীয় বিনিময়)](https://offschool.site/subjects/biology/ch07/t04/)
  - [Topic: Diseases of the Respiratory Tract (শ্বাসনালী সংক্রান্ত রোগ)](https://offschool.site/subjects/biology/ch07/t05/)
  - [Topic: Asthma (অ্যাজমা)](https://offschool.site/subjects/biology/ch07/t06/)
  - [Topic: Bronchitis (ব্রংকাইটিস)](https://offschool.site/subjects/biology/ch07/t07/)
  - [Topic: Pneumonia (নিউমোনিয়া)](https://offschool.site/subjects/biology/ch07/t08/)
  - [Topic: Tuberculosis (যক্ষ্মা)](https://offschool.site/subjects/biology/ch07/t09/)
  - [Topic: Lung cancer (ফুসফুসের ক্যান্সার)](https://offschool.site/subjects/biology/ch07/t10/)
  - [Simulation: Breathing mechanism and Boyle's law: Lung pressure and airflow (শ্বাস-প্রশ্বাস প্রক্রিয়া ও বয়েলের সূত্র: ফুসফুসে বায়ুর চাপ ও প্রবাহ)](https://offschool.site/sim/ssc.biology.ch07.breathing-model/): In science class, Rafi places a hand on his chest, takes a deep breath, and notices his chest expand. At rest, the initial lung volume is 3.0 L and internal air pressure equals atmospheric pressure (760 mmHg). During inhalation, the diaphragm contracts and flattens downward, expanding the thoracic cavity and increasing lung volume by 0.5 L to 3.5 L. Just before outside air rushes into the lungs, what will the intra-pulmonary air pressure be?
  - [Simulation: What does a leaf give out in the dark? (অন্ধকারে পাতা কী ছাড়ে?)](https://offschool.site/sim/ssc.biology.ch07.leaf-in-indicator/): In the biology lab, Arif puts red hydrogen carbonate indicator in two tubes, adds a living leaf to each and seals them. One tube goes under a lamp, the other is wrapped in foil in the dark. The indicator turns yellow when CO₂ rises and purple when it falls. After two hours, what colour is the tube in the dark?
- [Chapter 8: Excretory System (রেচন প্রক্রিয়া)](https://offschool.site/subjects/biology/ch08/)
  - [Topic: Human Excretion (মানব রেচন)](https://offschool.site/subjects/biology/ch08/t01/)
  - [Topic: Excretory Substances (রেচন পদার্থ)](https://offschool.site/subjects/biology/ch08/t02/)
  - [Topic: Excretory substance: urea (রেচন পদার্থ: ইউরিয়া)](https://offschool.site/subjects/biology/ch08/t03/)
  - [Topic: Excretory substance: salts (রেচন পদার্থ: লবণ)](https://offschool.site/subjects/biology/ch08/t04/)
  - [Topic: Excretory substance: nitrogenous waste (রেচন পদার্থ: নাইট্রোজেনঘটিত বর্জ্য)](https://offschool.site/subjects/biology/ch08/t05/)
  - [Topic: Excretory substance: carbon dioxide (রেচন পদার্থ: কার্বন ডাই-অক্সাইড)](https://offschool.site/subjects/biology/ch08/t06/)
  - [Topic: The kidney (বৃক্ক (Kidney))](https://offschool.site/subjects/biology/ch08/t07/)
  - [Topic: Structure and function of the kidney (বৃক্কের গঠন ও কাজ)](https://offschool.site/subjects/biology/ch08/t08/)
  - [Topic: Nephron (নেফ্রন)](https://offschool.site/subjects/biology/ch08/t09/)
  - [Topic: Structure and function of the nephron (নেফ্রনের গঠন ও কাজ)](https://offschool.site/subjects/biology/ch08/t10/)
  - [Topic: Role of the Kidney in Osmoregulation (অসমোরেগুলেশনে বৃক্কের ভূমিকা)](https://offschool.site/subjects/biology/ch08/t11/)
  - [Topic: Kidney Problems (বৃক্কের সমস্যা)](https://offschool.site/subjects/biology/ch08/t12/)
  - [Topic: Kidney Stones: Remedy (বৃক্কে পাথর: প্রতিকার)](https://offschool.site/subjects/biology/ch08/t13/)
  - [Topic: Acute Kidney Failure: Symptoms and What to Do (তাৎক্ষণিক বৃক্ক বিকল: লক্ষণ ও করণীয়)](https://offschool.site/subjects/biology/ch08/t14/)
  - [Topic: Dialysis (ডায়ালাইসিস)](https://offschool.site/subjects/biology/ch08/t15/)
  - [Topic: Kidney transplantation and posthumous kidney donation (বৃক্ক প্রতিস্থাপন এবং মরণোত্তর বৃক্ক দান)](https://offschool.site/subjects/biology/ch08/t16/)
  - [Topic: Urinary Tract Diseases and Ways to Keep it Healthy (মূত্রনালীর রোগ ও সুস্থ রাখার উপায়)](https://offschool.site/subjects/biology/ch08/t17/)
  - [Simulation: Why is glucose put in dialysis fluid? (ডায়ালাইসিস তরলে গ্লুকোজ কেন রাখা হয়?)](https://offschool.site/sim/ssc.biology.ch08.kidney-dialysis/): With failed kidneys, Uncle Karim has dialysis three times a week. In the machine his blood flows past a thin membrane with dialysis fluid on the other side. The fluid carries a normal blood level of glucose. If it carried no glucose, what would happen to the glucose in his blood?
  - [Simulation: Filtration and Reabsorption in the Nephron (নেফ্রনে রক্তের পরিস্রাবণ ও পুনঃশোষণ)](https://offschool.site/sim/ssc.biology.ch08.kidney-filtration/): In a healthy human, about 1200 L of blood flows through the kidneys daily, and 15% of it, 180 L of fluid, is filtered into Bowman's capsule. If 99% of this filtered water and useful solutes are reabsorbed back into the blood along the renal tubules, how many litres of urine will be formed per day?
- [Chapter 9: Firmness and Locomotion (দৃঢ়তা প্রদান ও চলন)](https://offschool.site/subjects/biology/ch09/)
  - [Topic: General Introduction to the Human Skeleton (মানব কঙ্কালের সাধারণ পরিচিতি)](https://offschool.site/subjects/biology/ch09/t01/)
  - [Topic: Role of the Skeleton in Firmness and Locomotion (দৃঢ়তা প্রদান এবং চলনে কঙ্কালের ভূমিকা)](https://offschool.site/subjects/biology/ch09/t02/)
  - [Topic: Bone (অস্থি)](https://offschool.site/subjects/biology/ch09/t03/)
  - [Topic: Major Bones (প্রধান অস্থি)](https://offschool.site/subjects/biology/ch09/t04/)
  - [Topic: Cartilage (তরুণাস্থি)](https://offschool.site/subjects/biology/ch09/t05/)
  - [Topic: Joints and their functions: the synovial joint (অস্থিসন্ধি ও এর কাজ: সাইনোভিয়াল অস্থিসন্ধি)](https://offschool.site/subjects/biology/ch09/t06/)
  - [Topic: Muscle Action (পেশির ক্রিয়া)](https://offschool.site/subjects/biology/ch09/t07/)
  - [Topic: Tendon and Ligament (টেনডন ও লিগামেন্ট)](https://offschool.site/subjects/biology/ch09/t08/)
  - [Topic: Osteoporosis (অস্টিওপোরোসিস)](https://offschool.site/subjects/biology/ch09/t09/)
  - [Topic: Causes of osteoporosis (অস্টিওপোরোসিসের কারণ)](https://offschool.site/subjects/biology/ch09/t10/)
  - [Topic: Symptoms of osteoporosis (অস্টিওপোরোসিসের লক্ষণ)](https://offschool.site/subjects/biology/ch09/t11/)
  - [Topic: Remedies for osteoporosis (অস্টিওপোরোসিসের প্রতিকার)](https://offschool.site/subjects/biology/ch09/t12/)
  - [Topic: Arthritis (আর্থ্রাইটিস)](https://offschool.site/subjects/biology/ch09/t13/)
  - [Topic: Causes of arthritis (আর্থ্রাইটিসের কারণ)](https://offschool.site/subjects/biology/ch09/t14/)
  - [Topic: Symptoms of arthritis (আর্থ্রাইটিসের লক্ষণ)](https://offschool.site/subjects/biology/ch09/t15/)
  - [Topic: Remedies for arthritis (আর্থ্রাইটিসের প্রতিকার)](https://offschool.site/subjects/biology/ch09/t16/)
  - [Simulation: Forearm and biceps muscle: Third-class lever (হাতের কনুই ও পেশির টান: তৃতীয় শ্রেণির লিভার)](https://offschool.site/sim/ssc.biology.ch09.arm-lever/): Siam stands with his elbow bent and forearm horizontal. The elbow joint acts as the fulcrum, and the biceps tendon inserts onto the radius bone 3 cm from the elbow (effort arm). The palm is 30 cm from the elbow (load arm). Holding a 1 kg object (weight 9.8 N) requires the biceps to exert 98 N of force to keep the arm steady. If Siam now holds a 5 kg watermelon (weight 49 N) at the same position, what pull force must the biceps exert? Will this muscle force be greater or less than the watermelon's weight?
- [Chapter 10: Coordination (সমন্বয়)](https://offschool.site/subjects/biology/ch10/)
  - [Topic: Coordination in Plants (উদ্ভিদে সমন্বয়)](https://offschool.site/subjects/biology/ch10/t01/)
  - [Topic: Growth in plants (উদ্ভিদের বৃদ্ধি)](https://offschool.site/subjects/biology/ch10/t02/)
  - [Topic: Movement in plants (উদ্ভিদের চলন)](https://offschool.site/subjects/biology/ch10/t03/)
  - [Topic: Coordination in Animals (প্রাণীর সমন্বয় প্রক্রিয়া)](https://offschool.site/subjects/biology/ch10/t04/)
  - [Topic: Nervous coordination (স্নায়ুবিক সমন্বয়)](https://offschool.site/subjects/biology/ch10/t05/)
  - [Topic: Hormonal coordination (হরমোনজনিত সমন্বয়)](https://offschool.site/subjects/biology/ch10/t06/)
  - [Topic: Main Parts and Functions of Nervous System (স্নায়ুতন্ত্রের প্রধান অংশ এবং কাজ)](https://offschool.site/subjects/biology/ch10/t07/)
  - [Topic: Structure and Function of a Neuron (সাধারণ নিউরনের গঠন ও কাজ)](https://offschool.site/subjects/biology/ch10/t08/)
  - [Topic: Reflex Action (প্রতিবর্তী প্রতিক্রিয়া)](https://offschool.site/subjects/biology/ch10/t09/)
  - [Topic: Impulse Transmission (আবেগ সঞ্চালন (Impulse Transmission))](https://offschool.site/subjects/biology/ch10/t10/)
  - [Topic: Hormone (প্রাণরস (Hormone))](https://offschool.site/subjects/biology/ch10/t11/)
  - [Topic: Abnormalities due to Hormone (প্রাণরস জনিত অস্বাভাবিকতা)](https://offschool.site/subjects/biology/ch10/t12/)
  - [Topic: Thyroid Problem (থাইরয়েড সমস্যা)](https://offschool.site/subjects/biology/ch10/t13/)
  - [Topic: Diabetes - Function of Insulin (বহুমূত্র (Diabetes) - ইনসুলিনের কার্যকারিতা)](https://offschool.site/subjects/biology/ch10/t14/)
  - [Topic: Stroke (স্ট্রোক)](https://offschool.site/subjects/biology/ch10/t15/)
  - [Topic: Causes and symptoms of stroke (স্ট্রোকের কারণ ও লক্ষণ)](https://offschool.site/subjects/biology/ch10/t16/)
  - [Topic: What to do immediately after a stroke (স্ট্রোক হলে তাৎক্ষণিক করণীয়)](https://offschool.site/subjects/biology/ch10/t17/)
  - [Topic: Ways to prevent stroke (স্ট্রোক প্রতিরোধের উপায়)](https://offschool.site/subjects/biology/ch10/t18/)
  - [Topic: Physical Problems due to Nervous Disorders (স্নায়ুবিক বৈকল্যজনিত শারীরিক সমস্যা)](https://offschool.site/subjects/biology/ch10/t19/)
  - [Topic: Paralysis (প্যারালাইসিস)](https://offschool.site/subjects/biology/ch10/t20/)
  - [Topic: Epilepsy (এপিলেপসি (মৃগীরোগ))](https://offschool.site/subjects/biology/ch10/t21/)
  - [Topic: Parkinson's disease (পারকিনসন রোগ)](https://offschool.site/subjects/biology/ch10/t22/)
  - [Topic: Influence of Tobacco and Drugs on Coordination (সমন্বয় কার্যক্রমে তামাক ও মাদকদ্রব্যের প্রভাব)](https://offschool.site/subjects/biology/ch10/t23/)
  - [Simulation: What happens in diabetes without insulin? (ইনসুলিন ছাড়া ডায়াবেটিসে কী হয়?)](https://offschool.site/sim/ssc.biology.ch10.diabetes-insulin-dose/): Fourteen-year-old Tania has type 1 diabetes: her pancreas can't make insulin. One day she eats rice at lunch without her insulin injection. Two hours later, what will her blood glucose be like?
  - [Simulation: When does the lojjaboti open again? (লজ্জাবতী আবার কখন খোলে?)](https://offschool.site/sim/ssc.biology.ch10.lojjaboti-touch/): In Ramna Park, the moment Tuhin touches a lojjaboti (touch-me-not), its leaflets fold shut. He worries he has damaged them. How is this different from a seedling slowly bending to the sun, and will the leaflets open again?
  - [Simulation: Reflex arc: Rapid response to touching a hot object (প্রতিবর্ত চক্র: উত্তপ্ত পাত্রে তাৎক্ষণিক সাড়া)](https://offschool.site/sim/ssc.biology.ch10.reflex-arc/): While working in the kitchen, Tania, a class ten student, accidentally touched a hot pan on the stove. Before she could even realize what was happening, her hand pulled away in the blink of an eye! A simple reflex arc consists of 5 main components. This reflex action took only 50 ms (0.05 s) to withdraw her hand, whereas conscious thinking by the human brain takes about 250 ms to make a decision. In this rapid reflex action, which center actually issued the immediate command to pull the hand away?
  - [Simulation: What brings blood sugar down after rice? (ভাত খাওয়ার পর রক্তের চিনি কে নামায়?)](https://offschool.site/sim/ssc.biology.ch10.rice-meal-insulin/): After a plate of rice at lunch, Rafi's blood glucose rises, yet within two hours it is nearly back to normal. How does that happen with no medicine? Which hormone, from where, brings the glucose down?
  - [Simulation: Will a seedling still bend to the window if its tip is covered? (ডগা ঢাকলে চারা কি আর জানালার দিকে বাঁকবে?)](https://offschool.site/sim/ssc.biology.ch10.seedling-at-the-window/): The mustard seedlings in a pot by Rina's window all lean towards the window. She puts a small cap of aluminium foil over the tip of one seedling and leaves the rest of the shoot uncovered. After a day, will this seedling bend towards the window?
- [Chapter 11: Reproduction in Organism (জীবের প্রজনন)](https://offschool.site/subjects/biology/ch11/)
  - [Topic: Reproduction in organisms (plants and animals) (জীবের (উদ্ভিদ ও প্রাণী) প্রজনন)](https://offschool.site/subjects/biology/ch11/t01/)
  - [Topic: Concept of reproduction (প্রজননের ধারণা)](https://offschool.site/subjects/biology/ch11/t02/)
  - [Topic: Importance of reproduction (প্রজননের গুরুত্ব)](https://offschool.site/subjects/biology/ch11/t03/)
  - [Topic: The flower: the reproductive organ of plants (উদ্ভিদের প্রজনন অঙ্গ-ফুল)](https://offschool.site/subjects/biology/ch11/t04/)
  - [Topic: Sexual reproduction in flowering plants (সপুষ্পক উদ্ভিদের যৌন প্রজনন)](https://offschool.site/subjects/biology/ch11/t05/)
  - [Topic: Asexual and sexual reproduction in animals (প্রাণীর অযৌন ও যৌন প্রজনন)](https://offschool.site/subjects/biology/ch11/t06/)
  - [Topic: Modes of reproduction (প্রজনন প্রকৃতি (Mode of reproduction))](https://offschool.site/subjects/biology/ch11/t07/)
  - [Topic: External and internal fertilisation (বহিঃ ও অন্তঃ নিষেক)](https://offschool.site/subjects/biology/ch11/t08/)
  - [Topic: Human reproduction (মানব প্রজনন)](https://offschool.site/subjects/biology/ch11/t09/)
  - [Topic: Role of hormones in human reproduction (মানব প্রজনন কার্যক্রমে প্রাণরসের (hormone) ভূমিকা)](https://offschool.site/subjects/biology/ch11/t10/)
  - [Topic: Development of the human embryo (মানব ভ্রুণের বিকাশ)](https://offschool.site/subjects/biology/ch11/t11/)
  - [Topic: AIDS infection in the body (দেহে এইডস এর সংক্রমণ)](https://offschool.site/subjects/biology/ch11/t12/)
  - [Topic: AIDS and the body's immune system (এইডস ও দেহের প্রতিরোধ ব্যবস্থা)](https://offschool.site/subjects/biology/ch11/t13/)
  - [Simulation: From mango flower to fruit and seed (আমের ফুল থেকে ফল ও বীজ সৃষ্টি)](https://offschool.site/sim/ssc.biology.ch11.flower-to-seed/): In early spring, visiting a mango orchard in Rajshahi, tenth-grader Orko noticed abundant clusters of mango blossoms. Honeybees were buzzing among the tiny flowers, collecting nectar and pollen. The teacher explained that pollination and fertilisation would transform these flowers into fruits. A few weeks later, the petals and stamens had withered and fallen, and small green fruitlets were swelling into mangoes, each containing a hard stone inside. In this sexual reproduction sequence, which part of the flower primarily transforms and enlarges into the sweet, fleshy edible mango fruit?
  - [Simulation: Why can someone with HIV look healthy for years? (এইচআইভি থাকলেও কেন বছরের পর বছর সুস্থ দেখায়?)](https://offschool.site/sim/ssc.biology.ch11.hiv-and-t-cells/): A migrant worker's blood test shows HIV, yet he is working well and feels fine. His brother thinks that if he isn't ill he needs no treatment. Without any treatment, when would AIDS appear?
- [Chapter 12: Heredity in Organisms and Biological Evolution (জীবের বংশগতি ও জৈব অভিব্যক্তি)](https://offschool.site/subjects/biology/ch12/)
  - [Topic: Concept of heredity (বংশগতির ধারণা)](https://offschool.site/subjects/biology/ch12/t01/)
  - [Topic: Materials that carry characteristics from generation to generation (বংশ পরম্পরায় চারিত্রিক বৈশিষ্ট্য বহনকারী উপাদান)](https://offschool.site/subjects/biology/ch12/t02/)
  - [Topic: Chromosome (ক্রোমোজোম)](https://offschool.site/subjects/biology/ch12/t03/)
  - [Topic: DNA (ডিএনএ)](https://offschool.site/subjects/biology/ch12/t04/)
  - [Topic: RNA (আরএনএ)](https://offschool.site/subjects/biology/ch12/t05/)
  - [Topic: Gene (জিন)](https://offschool.site/subjects/biology/ch12/t06/)
  - [Topic: Transfer of hereditary information and DNA replication (বংশগতির তথ্য স্থানান্তর এবং ডিএনএ প্রতিরূপ (replication))](https://offschool.site/subjects/biology/ch12/t07/)
  - [Topic: Need for DNA tests (ডিএনএ টেস্ট এর প্রয়োজনীয়তা)](https://offschool.site/subjects/biology/ch12/t08/)
  - [Topic: Sex determination in humans (মানুষের লিঙ্গ নির্ধারণ)](https://offschool.site/subjects/biology/ch12/t09/)
  - [Topic: Genetic disorders (জেনেটিক ডিসঅর্ডার)](https://offschool.site/subjects/biology/ch12/t10/)
  - [Topic: Colour blindness (বর্ণান্ধতা)](https://offschool.site/subjects/biology/ch12/t11/)
  - [Topic: Thalassaemia (থ্যালাসেমিয়া)](https://offschool.site/subjects/biology/ch12/t12/)
  - [Topic: Evolution (বিবর্তন)](https://offschool.site/subjects/biology/ch12/t13/)
  - [Topic: Origin of life (জীবনের আবির্ভাব)](https://offschool.site/subjects/biology/ch12/t20/)
  - [Topic: Variation in the living world (জীবজগতের ভিন্নতা)](https://offschool.site/subjects/biology/ch12/t14/)
  - [Topic: Tendency to overproduce (অত্যধিক প্রজননের প্রবণতা)](https://offschool.site/subjects/biology/ch12/t15/)
  - [Topic: Struggle for existence (জীবের বাঁচার সংগ্রাম)](https://offschool.site/subjects/biology/ch12/t16/)
  - [Topic: Natural selection (প্রকৃতিগত নির্বাচন)](https://offschool.site/subjects/biology/ch12/t17/)
  - [Topic: Survival of the fittest (যোগ্যতমের টিকে থাকা)](https://offschool.site/subjects/biology/ch12/t18/)
  - [Topic: Evidence of biological evolution (জৈব অভিব্যক্তির প্রমাণসমূহ)](https://offschool.site/subjects/biology/ch12/t21/)
  - [Topic: Importance of evolution in the survival of species (প্রজাতির টিকে থাকায় বিবর্তনের গুরুত্ব)](https://offschool.site/subjects/biology/ch12/t19/)
  - [Simulation: Healthy parents, yet two colour-blind brothers? (বাবা-মা সুস্থ, তবু দুই ভাই বর্ণান্ধ?)](https://offschool.site/sim/ssc.biology.ch12.colour-blind-brothers/): Two brothers in Sylhet can't tell red from green, though their parents and sister can. The doctor says their mother is a carrier of the gene. For a carrier mother and a normal father, what is the chance that a son is colour blind, and a daughter?
  - [Simulation: After three copies, where are the old strands? (তিনবার কপির পর পুরোনো সূত্রক কোথায়?)](https://offschool.site/sim/ssc.biology.ch12.dna-copies-itself/): Before a cell divides, its DNA makes a copy of itself so that both daughter cells get the same hereditary information. One DNA molecule copied three times gives 8 molecules. How many of those 8 still carry one of the starting molecule's original strands?
  - [Simulation: How much must a DNA test match? (DNA পরীক্ষায় কতটা মিল লাগে?)](https://offschool.site/sim/ssc.biology.ch12.dna-test-paternity/): In a family court, it is disputed who a child's father is. Six regions of DNA are tested for three men, the mother and the child. A lawyer says the man who matches in most regions must be the father. Is that how a DNA test decides?
  - [Simulation: How is a gene's message written into RNA? (জিনের বার্তা RNA তে কীভাবে লেখা হয়?)](https://offschool.site/sim/ssc.biology.ch12.dna-to-rna-copy/): In class, Nusrat cuts out a paper DNA ladder. One strand reads TACGGTCAT. The teacher says the cell makes an mRNA copy from this strand to carry the instructions for making a protein. Which letters will that mRNA copy have?
  - [Simulation: Mendel's Monohybrid Cross: Tall and Short Pea Plants (মেন্ডেলের মনোহাইব্রিড ক্রস: লম্বা ও খাটো মটরশুঁটি)](https://offschool.site/sim/ssc.biology.ch12.mendel-cross/): In a school biology garden, seeds are collected by cross-pollinating two hybrid tall pea plants (Aa × Aa). In pea plants, the tall allele (A) is dominant over the dwarf allele (a). Arpita thinks: 'Since both parents are tall, all offspring will be tall.' Shanto thinks: 'No, because both are hybrids, half will be tall and half short (1:1).' In a small sample of 10 seedlings, random variation causes fluctuations. What will be the phenotypic ratio of tall to short pea plants when observing a large number of offspring?
  - [Simulation: Natural Selection in Paddy Fields: Grasshopper Adaptation (সবুজ ধানের ক্ষেতে প্রাকৃতিক নির্বাচন: ঘাসফড়িংয়ের অভিযোজন)](https://offschool.site/sim/ssc.biology.ch12.paddy-grasshopper-selection/): In a lush green aman paddy field in Mymensingh, a population of grasshoppers lives among the rice plants. Initially, due to natural variation, only 20% (0.20) of the grasshoppers are green while the remaining 80% (0.80) are brown. Green grasshoppers camouflage against the green paddy leaves, so predatory birds like drongos and mynahs rarely spot them. Consequently, their survival rate each generation is 0.8 (80%). In contrast, visible brown grasshoppers stand out against the green leaves, giving them a survival rate of only 0.4 (40%). With this camouflage advantage, what will be the expected proportion of green grasshoppers in the population after 4 generations?
  - [Simulation: Thalassemia Carrier Cross: Disease Risk from Parents to Offspring (থ্যালাসেমিয়ার বাহক ক্রস: মা-বাবা থেকে সন্তানে রোগের ঝুঁকি)](https://offschool.site/sim/ssc.biology.ch12.thalassaemia-carrier-cross/): At a health centre in Faridpur, a blood test reveals that Rahim is an asymptomatic carrier of thalassemia (Aa). Thalassemia is an autosomal recessive disorder where the normal allele (A) is dominant over the thalassemia allele (a). If Rahim marries a normal non-carrier woman (AA), none of their children will have the disease (theoretical probability of being disease-free is 1.00 or 100%). But if Rahim marries Salma, who is also a healthy carrier (Aa), what is the theoretical probability that their child will be disease-free (dominant phenotype A_)?
  - [Simulation: Sex Determination: Boy or Girl? (সন্তানের লিঙ্গ নির্ধারণ: ছেলে নাকি মেয়ে?)](https://offschool.site/sim/ssc.biology.ch12.who-decides-boy-or-girl/): In many families, the mother is unfairly blamed when daughters are born. A family has had three daughters in a row. A relative said: 'Three girls were born in a row, so the chance of the fourth child being a boy is much higher now.' Another said: 'Whether the child is a boy or a girl depends entirely on the mother.' In reality, all maternal eggs carry an X chromosome, while half of paternal sperm carry X and half carry Y. What is the true theoretical probability that the fourth child is a boy?
- [Chapter 13: Environment of Life (জীবের পরিবেশ)](https://offschool.site/subjects/biology/ch13/)
  - [Topic: Ecosystem (বাস্তুতন্ত্র)](https://offschool.site/subjects/biology/ch13/t01/)
  - [Topic: Concept of an ecosystem (বাস্তুতন্ত্রের ধারণা)](https://offschool.site/subjects/biology/ch13/t02/)
  - [Topic: Components of an ecosystem and their relationships (বাস্তুতন্ত্রের উপাদান এবং এদের সম্পর্ক)](https://offschool.site/subjects/biology/ch13/t03/)
  - [Topic: Food Chain and Food Web (খাদ্যশৃঙ্খল ও খাদ্যজাল)](https://offschool.site/subjects/biology/ch13/t04/)
  - [Topic: Energy Flow and Relationship of Nutrients in Ecosystem (বাস্তুতন্ত্রে শক্তির প্রবাহ ও পুষ্টি উপাদানের সম্পর্ক)](https://offschool.site/subjects/biology/ch13/t05/)
  - [Topic: Trophic Levels and Relationship of Energy (ট্রফিক লেভেল ও শক্তির সম্পর্ক)](https://offschool.site/subjects/biology/ch13/t06/)
  - [Topic: Concept of Energy Pyramid and Its Effect to Keep Food Chains in Limit (শক্তি পিরামিডের ধারণা এবং খাদ্য শিকল সীমিত করতে এর প্রভাব)](https://offschool.site/subjects/biology/ch13/t07/)
  - [Topic: Biodiversity and Its Types (জীববৈচিত্র্য এবং এর প্রকারভেদ)](https://offschool.site/subjects/biology/ch13/t08/)
  - [Topic: Effect of Biodiversity on the Maintenance of Stability in an Ecosystem (বাস্তুতন্ত্রের স্থিতিশীলতা রক্ষায় জীববৈচিত্র্যের প্রভাব)](https://offschool.site/subjects/biology/ch13/t09/)
  - [Topic: Interaction and Interdependence Among Different Organisms and the Balance of Environment (বিভিন্ন জীবের মধ্যে মিথস্ক্রিয়া, আন্তঃ নির্ভরশীলতা ও পরিবেশের ভারসাম্যতা)](https://offschool.site/subjects/biology/ch13/t10/)
  - [Topic: Significance and Methods of Conserving Environment (পরিবেশ সংরক্ষণের পদ্ধতি ও গুরুত্ব)](https://offschool.site/subjects/biology/ch13/t11/)
  - [Simulation: Energy Flow and Energy Pyramid in a Pond (পুকুরের খাদ্যশৃঙ্খলে শক্তি প্রবাহ ও শক্তি পিরামিড)](https://offschool.site/sim/ssc.biology.ch13.energy-pyramid/): In a pond food chain, about 10% of energy transfers at each trophic level: phytoplankton (producer) → small fish (1st consumer) → big fish (2nd consumer) → heron (top consumer), while 90% is lost to respiration and heat. With 1000 J in phytoplankton, the heron receives 1 J. If the phytoplankton's energy increases to 10,000 J, how many joules (J) will the heron receive?
  - [Simulation: Why is a forest with more species more secure? (বেশি প্রজাতি থাকলে বন কেন টেকসই?)](https://offschool.site/sim/ssc.biology.ch13.more-species-more-stable/): A disease kills every deer in the Sundarbans. In one forest deer are the tigers' only food; in another there are wild boar as well. Twenty years later, how are the tigers doing in each forest?
  - [Simulation: What would happen to the Sundarbans without tigers? (বাঘ না থাকলে সুন্দরবনের কী হবে?)](https://offschool.site/sim/ssc.biology.ch13.sundarbans-without-tigers/): In the Sundarbans tigers eat deer, and deer eat leaves and grass. Some say that without tigers the deer would flourish safely and the forest would look even better. If every tiger were gone, what would the deer and the plants be like five years later?
- [Chapter 14: Biotechnology (জীবপ্রযুক্তি)](https://offschool.site/subjects/biology/ch14/)
  - [Topic: Biotechnology (জীবপ্রযুক্তি (Biotechnology))](https://offschool.site/subjects/biology/ch14/t01/)
  - [Topic: Concept and importance of biotechnology (জীবপ্রযুক্তির ধারণা ও গুরুত্ব)](https://offschool.site/subjects/biology/ch14/t02/)
  - [Topic: Tissue culture and its uses (টিস্যু কালচার এবং এর ব্যবহার)](https://offschool.site/subjects/biology/ch14/t03/)
  - [Topic: Genetic engineering (জেনেটিক ইঞ্জিনিয়ারিং)](https://offschool.site/subjects/biology/ch14/t04/)
  - [Topic: Aims of genetic engineering (জেনেটিক ইঞ্জিনিয়ারিংয়ের উদ্দেশ্য)](https://offschool.site/subjects/biology/ch14/t05/)
  - [Topic: Uses of genetic engineering (জেনেটিক ইঞ্জিনিয়ারিং এর ব্যবহার)](https://offschool.site/subjects/biology/ch14/t06/)
  - [Topic: Genetic engineering in crop improvement (শস্য উন্নয়নে জেনেটিক ইঞ্জিনিয়ারিং)](https://offschool.site/subjects/biology/ch14/t07/)
  - [Topic: Genetic engineering in curing diseases of domestic animals (গৃহপালিত পশুর রোগ নিরাময়ে জেনেটিক ইঞ্জিনিয়ারিং)](https://offschool.site/subjects/biology/ch14/t08/)
  - [Topic: Genetic engineering in producing insulin and hormones (ইনসুলিন ও হরমোন উৎপাদনে জেনেটিক ইঞ্জিনিয়ারিং)](https://offschool.site/subjects/biology/ch14/t09/)
  - [Simulation: Human insulin from bacteria: Recombinant DNA technology (ব্যাকটেরিয়া থেকে মানব ইনসুলিন উৎপাদন: রিকম্বিন্যান্ট ডিএনএ প্রযুক্তি)](https://offschool.site/sim/ssc.biology.ch14.insulin-from-bacteria/): In Bangladesh, around 13 million people suffer from diabetes. According to doctors at BIRDEM Hospital in Dhaka, many patients require daily insulin injections to control blood glucose levels. Insulin is a protein hormone composed of 51 amino acids, with 21 amino acids in chain A and 30 in chain B. In the past, insulin was extracted from cattle and pig pancreases, which was expensive and caused severe allergic reactions in patients. Today, using recombinant DNA technology, harmless E. coli bacteria produce 100% pure human insulin in factories. After inserting the human insulin gene into the bacterial plasmid, how can a single-celled bacterium synthesize human insulin containing the exact 51 amino acids just like human cells?
  - [Simulation: Plant tissue culture: Producing identical plantlets from explant (উদ্ভিদ টিস্যু কালচার: এক্সপ্লান্ট থেকে অবিকল চারা উৎপাদন)](https://offschool.site/sim/ssc.biology.ch14.tissue-culture/): A farmer in Narsingdi wants to establish a commercial banana orchard of the premium 'Amritsagar' variety. Planting traditional suckers carries high risks of Panama disease and Banana bunchy top virus, along with uneven fruit yields. Therefore, he procured 10,000 tissue-cultured banana plantlets developed by a BARI biotechnology laboratory from the apical bud (explant) of a single, disease-free, high-yielding mother plant. Months later, all 10,000 banana plants grew with identical height, sweetness, disease resistance, and fruit yield: every plant was genetically identical (a somaclone). Unlike natural sexual reproduction where seeds produce genetic variation, why are all plantlets produced through plant tissue culture genetically identical to the mother plant?

## Higher Math (উচ্চতর গণিত)

Sets and functions, equations, geometry, inequalities, series, trigonometry, logarithms, the binomial theorem, coordinate geometry, vectors and probability, on graphs and drawings.

- [SSC Higher Math](https://offschool.site/subjects/higher-math/): সেট ও ফাংশন, সমীকরণ, জ্যামিতি, অসমতা, অসীম ধারা, ত্রিকোণমিতি, লগারিদম, দ্বিপদী বিস্তৃতি, স্থানাঙ্ক জ্যামিতি, ভেক্টর ও সম্ভাবনা, গ্রাফে আর আঁকায় দেখো।
- [SSC Higher Math formula sheet](https://offschool.site/subjects/higher-math/formulas/): every formula, chapter by chapter, each with its simulation.
- [Chapter 1: Set and Function (সেট ও ফাংশন)](https://offschool.site/subjects/higher-math/ch01/)
  - [Topic: Universal set, subset, complement set and power set (সার্বিক সেট, উপসেট, পূরক সেট ও শক্তি সেট)](https://offschool.site/subjects/higher-math/ch01/t01/)
  - [Topic: Union, intersection and difference of sets (সেটের সংযোগ, ছেদ ও অন্তর)](https://offschool.site/subjects/higher-math/ch01/t02/)
  - [Topic: Properties of set operations (সেট প্রক্রিয়ার ধর্মাবলি)](https://offschool.site/subjects/higher-math/ch01/t03/)
  - [Topic: Equivalent sets and infinite sets (সমতুল সেট ও অসীম সেট)](https://offschool.site/subjects/higher-math/ch01/t04/)
  - [Topic: Power set of a union of sets (সেটের সংযোগের শক্তি সেট)](https://offschool.site/subjects/higher-math/ch01/t05/)
  - [Topic: Sets in solving real problems (বাস্তব সমস্যা সমাধানে সেট)](https://offschool.site/subjects/higher-math/ch01/t06/)
  - [Topic: Concept of relation and function (অন্বয় এবং ফাংশন এর ধারণা)](https://offschool.site/subjects/higher-math/ch01/t07/)
  - [Topic: Domain and range of a function (ফাংশন এর ডোমেন ও রেঞ্জ)](https://offschool.site/subjects/higher-math/ch01/t08/)
  - [Topic: One-one function, onto function and one-one onto function (এক-এক ফাংশন, সার্বিক ফাংশন ও এক-এক সার্বিক ফাংশন)](https://offschool.site/subjects/higher-math/ch01/t09/)
  - [Topic: Inverse function; graphs of relations and functions (বিপরীত ফাংশন অন্বয় ও ফাংশনের লেখচিত্র)](https://offschool.site/subjects/higher-math/ch01/t10/)
  - [Simulation: Who plays which game? (কারা কোন খেলা খেলে?)](https://offschool.site/sim/ssc.higher-math.ch01.cricket-football-venn/): Of 40 students in class nine, 20 play cricket, 15 play football and 5 play both. How many play neither game?
  - [Simulation: Are (A ∪ B)′ and A′ ∩ B′ the same? ((A ∪ B)′ আর A′ ∩ B′ কি একই?)](https://offschool.site/sim/ssc.higher-math.ch01.de-morgan-multiples/): U = {1, 2, …, 30}. A is the multiples of 2, B the multiples of 3 and C the multiples of 5. Rumi says (A ∪ B)′ means numbers that are multiples of neither 2 nor 3, and A′ ∩ B′ means numbers that are not multiples of 2 and not multiples of 3; so they are the same set. Is she right?
  - [Simulation: Exam seat mapping from roll numbers (রোল নম্বর ও পরীক্ষার সিট বণ্টন)](https://offschool.site/sim/ssc.higher-math.ch01.exam-seat-mapping/): In a test seating arrangement, students have roll numbers {-2, -1, 0, 1, 2}. When seats are assigned using the rule f(x) = 2x + 1, 5 distinct seats are used. If the rule is changed to f(x) = x², how many distinct seats will actually be used (what is the size of the range)?
  - [Simulation: Locker Assignment: One-One and Onto Functions (লকার বণ্টন: এক-এক ও সার্বিক ফাংশন)](https://offschool.site/sim/ssc.higher-math.ch01.locker-one-one-onto/): A school assigns lockers to 5 students (rolls: −2, −1, 0, 1, 2) using f(x) = 2x + 1. Considering only the assigned lockers {−3, −1, 1, 3, 5}, each student gets a distinct locker and none is empty. But the locker room has 11 lockers in total, numbered −5 to 5. If all lockers form the codomain, will the function be onto?
  - [Simulation: Domain and range of a square-root function (বর্গমূল ফাংশনের ডোমেন ও রেঞ্জ)](https://offschool.site/sim/ssc.higher-math.ch01.square-root-domain/): Take the function f(x) = √(x − c). A negative number has no real square root, so f(x) has no real value when the expression under the root is negative. With c = 1, for which values of x is f(x) defined, that is, what is the domain of the function?
  - [Simulation: Tiffin box and power set (টিফিন বাক্স ও শক্তি সেট)](https://offschool.site/sim/ssc.higher-math.ch01.tiffin-power-set/): Mitu's mother packs any combination of three snacks: singara, samosa, and piyaju. On fasting days she may pack none, leaving the box empty. How many different tiffin boxes are possible from these 3 snacks?
- [Chapter 2: Algebraic Expression (বীজগাণিতিক রাশি)](https://offschool.site/subjects/higher-math/ch02/)
  - [Topic: Polynomials (বহুপদী)](https://offschool.site/subjects/higher-math/ch02/t01/)
  - [Topic: Homogeneous, symmetric and cyclic expressions (up to three variables) (সমমাত্রিক, প্রতিসম ও চক্র-ক্রমিক রাশি (অনূর্ধ্ব তিন চলক))](https://offschool.site/subjects/higher-math/ch02/t02/)
  - [Topic: Expressing rational fractions as partial fractions (simple rational fractions) (মূলদ ভগ্নাংশকে আংশিক ভগ্নাংশে প্রকাশ (সরল মূলদ ভগ্নাংশ))](https://offschool.site/subjects/higher-math/ch02/t03/)
  - [Simulation: Finding factors without division (ভাগ না করেই উৎপাদক নির্ণয়)](https://offschool.site/sim/ssc.higher-math.ch02.factor-theorem/): The volume of a box is given by the polynomial P(x) = x³ − 4x² + x + 6. Dividing by (x − 1) leaves a remainder of 4 (so P(1) = 4, meaning x − 1 is not a factor). If the divisor is (x − 3), what will the remainder be, and is (x − 3) a factor of P(x)?
  - [Simulation: Split the fraction in two (ভগ্নাংশটিকে দুই টুকরো করো)](https://offschool.site/sim/ssc.higher-math.ch02.split-the-fraction/): Before learning calculus, Tahsin finds that (5x − 1)/((x + 1)(x − 1)) can be written as the sum of two simple fractions, A/(x + 1) + B/(x − 1). What are A and B?
  - [Simulation: Is x²y + y²z + z²x symmetric? (x²y + y²z + z²x কি প্রতিসম?)](https://offschool.site/sim/ssc.higher-math.ch02.symmetric-or-cyclic/): Nadia notices that swapping any two letters in x² + y² + z² leaves it unchanged. Now she is looking at x²y + y²z + z²x. Is it symmetric, cyclic, both, or neither?
- [Chapter 3: Geometry (জ্যামিতি)](https://offschool.site/subjects/higher-math/ch04/)
  - [Topic: Orthogonal projection (লম্ব অভিক্ষেপ)](https://offschool.site/subjects/higher-math/ch04/t01/)
  - [Topic: Extensions of the theorem of Pythagoras (পিথাগোরাসের উপপাদ্যের বিস্তৃতি)](https://offschool.site/subjects/higher-math/ch04/t02/)
  - [Simulation: Sides and medians of a triangle (Apollonius's theorem) (ত্রিভুজের বাহু ও মধ্যমার সম্পর্ক (অ্যাপোলোনিয়াসের উপপাদ্য))](https://offschool.site/sim/ssc.higher-math.ch04.apollonius-median/): In a triangular boundary, base BC = 6 m with midpoint D (so BD = 3 m). Initially, vertex A is at (0, 4), giving median AD = 4 m and sum of squares AB² + AC² = 50. If vertex A is moved to (3, 4), the median increases to AD = 5 m. What will the sum of squares AB² + AC² be then?
  - [Simulation: Orthogonal projection of a leaning bamboo (খালের পাড়ে হেলানো বাঁশের লম্ব অভিক্ষেপ)](https://offschool.site/sim/ssc.higher-math.ch04.leaning-bamboo-projection/): On a canal bank, point B is at (−4, 0) and at the water edge C(2, 0), a bamboo pole CA leans out over the water. Under the noon sun, its orthogonal projection on the extended ground line is CD. With tip A at (6, 3), ∠C is an obtuse angle. Here BC = 6 and CA = 5, so BC² + CA² = 61. How does the square on the opposite side AB² compare with BC² + CA²?
- [Chapter 4: Geometric Constructions (জ্যামিতিক অঙ্কন)](https://offschool.site/subjects/higher-math/ch05/)
  - [Topic: Miscellaneous geometric constructions (বিবিধ জ্যামিতিক অঙ্কন)](https://offschool.site/subjects/higher-math/ch05/t01/)
  - [Topic: Relating to triangles (ত্রিভুজ সংক্রান্ত)](https://offschool.site/subjects/higher-math/ch05/t02/)
  - [Topic: Relating to circles (বৃত্ত সংক্রান্ত)](https://offschool.site/subjects/higher-math/ch05/t03/)
  - [Simulation: A tank on the road, equally far from two wells (দুই নলকূপ থেকে সমান দূরে, রাস্তার ওপর ট্যাংক)](https://offschool.site/sim/ssc.higher-math.ch05.tank-between-two-wells/): A village has two tube wells, P and Q. A water tank will stand on the straight road (the line y = k) at the same distance from both wells, so a circle centred on the tank passes through P and Q. What happens if Q is moved directly below P (the same x)?
  - [Simulation: Triangle construction and condition for existence (ত্রিভুজ অঙ্কন ও গঠনের শর্ত)](https://offschool.site/sim/ssc.higher-math.ch05.triangle-construction/): To build a triangular frame for the school science fair, the base length is set to a = 6 cm and a base angle to ∠B = 60°. With the sum of the other two sides s = 9 cm, the frame is successfully constructed (explore steps 1 to 7). If we decrease the combined length of the other two sides, at what length (in cm) or below does it become impossible to form the triangular frame?
- [Chapter 5: Equation (সমীকরণ)](https://offschool.site/subjects/higher-math/ch03/)
  - [Topic: Solution of quadratic equations (ax² + bx + c = 0) (দ্বিঘাত সমীকরণ (ax² + bx + c = 0) সমাধান)](https://offschool.site/subjects/higher-math/ch03/t01/)
  - [Topic: Equations involving square roots (বর্গমূলবিশিষ্ট সমীকরণ)](https://offschool.site/subjects/higher-math/ch03/t02/)
  - [Topic: Exponential equations (সূচকীয় সমীকরণ)](https://offschool.site/subjects/higher-math/ch03/t03/)
  - [Topic: Systems of linear and quadratic equations in two variables (দুই চলক একঘাত ও দ্বিঘাত সমীকরণের জোট)](https://offschool.site/subjects/higher-math/ch03/t04/)
  - [Topic: Systems of exponential equations in two variables (দুই চলকবিশিষ্ট সূচকীয় সমীকরণ জোট)](https://offschool.site/subjects/higher-math/ch03/t05/)
  - [Topic: Solving quadratic equations with the help of graphs (লেখচিত্রের সাহায্যে দ্বিঘাত সমীকরণ সমাধান)](https://offschool.site/subjects/higher-math/ch03/t06/)
  - [Simulation: Where a line meets a parabola (পরাবৃত্তের সাথে সরলরেখার ছেদ)](https://offschool.site/sim/ssc.higher-math.ch03.line-meets-parabola/): In the design of a pedestrian bridge, a curved girder follows the parabola y = x². Engineers placed a horizontal straight pipe below it along y = -1 (m = 0, p = -1), which does not touch the girder (0 intersections). If the pipe is raised straight up to y = 4 (p = 4) while keeping it horizontal, at how many points will it intersect the girder?
  - [Simulation: Rooftop garden plot and quadratic equation (ছাদবাগানের আয়তাকার প্লট ও দ্বিঘাত সমীকরণ)](https://offschool.site/sim/ssc.higher-math.ch03.rooftop-garden-quadratic/): A rooftop vegetable plot in Dhaka is 3 m longer than it is wide and has an area of 40 m²: x² + 3x − 40 = 0. At default c = 0 the area is 0 m². Setting c = -40 represents the 40 m² plot. What is the physical width x of the plot?
  - [Simulation: Does squaring sneak in a new root? (বর্গ করলে কি নতুন মূল ঢুকে পড়ে?)](https://offschool.site/sim/ssc.higher-math.ch03.square-root-trap/): To solve √(x + 5) = x − 1, Sakib squares both sides: x + 5 = x² − 2x + 1, so x² − 3x − 4 = 0, with roots x = 4 and x = −1. He writes both as answers. Do both satisfy the original equation?
- [Chapter 6: Inequality (অসমতা)](https://offschool.site/subjects/higher-math/ch06/)
  - [Topic: Linear inequalities in one and two variables (এক ও দুই চলকের এক ঘাতবিশিষ্ট অসমতা)](https://offschool.site/subjects/higher-math/ch06/t01/)
  - [Simulation: Budget and inequality solution region (বাজেট ও অসমতার সমাধান অঞ্চল)](https://offschool.site/sim/ssc.higher-math.ch06.budget-inequality/): At a shop, each pen costs Tk 20 and each notebook costs Tk 40. You have a total budget of Tk 200. For x pens and y notebooks, the budget inequality is 20x + 40y ≤ 200. Dividing both sides by 20 gives the simplified equivalent inequality: x + 2y ≤ 10 (a = 1, b = 2, c = 10). Initially, you plan to buy 2 pens and 2 notebooks (px = 2, py = 2, where x + 2y = 6 ≤ 10, costing Tk 120, which is within budget). If you want to buy 5 pens and 3 notebooks (px = 5, py = 3), what will the value of x + 2y be and will this plan fit within your Tk 200 budget?
- [Chapter 7: Infinite Series (অসীম ধারা)](https://offschool.site/subjects/higher-math/ch07/)
  - [Topic: Sequences (অনুক্রম)](https://offschool.site/subjects/higher-math/ch07/t01/)
  - [Topic: Infinite series (অসীম ধারা)](https://offschool.site/subjects/higher-math/ch07/t02/)
  - [Topic: Infinite geometric series (অসীম গুণোত্তর ধারা)](https://offschool.site/subjects/higher-math/ch07/t03/)
  - [Topic: Expressing a recurring decimal as an infinite geometric series and converting it into a common fraction (আবৃত্ত দশমিক সংখ্যাকে অনন্ত গুণোত্তর ধারায় প্রকাশ এবং সাধারণ ভগ্নাংশে রূপান্তর)](https://offschool.site/subjects/higher-math/ch07/t04/)
  - [Simulation: Bouncing tennis ball and sequence limits (টেনিস বলের বাউন্স ও অনুক্রমের সীমা)](https://offschool.site/sim/ssc.higher-math.ch07.bouncing-ball-sequence/): A tennis ball is dropped from a 10 m high school roof. Each time it bounces back to 60% (0.6) of its previous height: 10, 6, 3.6, ... Does the bounce height ever become exactly 0 m?
  - [Simulation: Halving the cake puzzle (অর্ধেক কেক খাওয়ার ধাঁধা)](https://offschool.site/sim/ssc.higher-math.ch07.halving-cake/): Arif has 1 whole birthday cake. First, he eats half of it (1/2). In the next step, he eats half of what remains (1/4), then half of the remainder again (1/8). If he keeps eating half of the remainder forever across infinitely many steps, what is the total amount eaten? Will the total ever exceed 1 whole cake?
  - [Simulation: Recurring decimals as infinite series (আবৃত্ত দশমিক ও অসীম ধারা)](https://offschool.site/sim/ssc.higher-math.ch07.recurring-decimal-series/): Dividing 1 taka by 3 on a shop calculator gives 0.3333... taka, which is an infinite geometric series: 0.3 + 0.03 + 0.003 + 0.0003 + ... Similarly, 0.999... can be written as 0.9 + 0.09 + 0.009 + ... (first term a = 0.9, common ratio r = 0.1). If we add these terms forever, will 0.999... equal exactly 1?
- [Chapter 8: Trigonometry (ত্রিকোণমিতি)](https://offschool.site/subjects/higher-math/ch08/)
  - [Topic: Radian measure (রেডিয়ান পরিমাপ)](https://offschool.site/subjects/higher-math/ch08/t01/)
  - [Topic: Relation between radian measure and degree measure (রেডিয়ান পরিমাপ ও ডিগ্রি পরিমাপের পারস্পরিক সম্পর্ক)](https://offschool.site/subjects/higher-math/ch08/t02/)
  - [Topic: Signs of the trigonometric ratios in the four quadrants (চারটি চর্তুভাগে ত্রিকোণমিতিক অনুপাতসমূহের চিহ্ন)](https://offschool.site/subjects/higher-math/ch08/t03/)
  - [Topic: Trigonometric ratios of angles up to 2π (অনূর্ধ্ব 2π কোণের ত্রিকোণমিতিক অনুপাত)](https://offschool.site/subjects/higher-math/ch08/t04/)
  - [Topic: Trigonometric ratios of the angle −θ (−θ কোণের ত্রিকোণমিতিক অনুপাত)](https://offschool.site/subjects/higher-math/ch08/t05/)
  - [Topic: Finding and applying the trigonometric ratios of the angles (nπ/2 ± θ) for integers n (n ≤ 4) (পূর্ণসংখ্যা n (n ≤ 4)-এর জন্য (nπ/2 ± θ) কোণের ত্রিকোণমিতিক অনুপাত নির্ণয় ও প্রয়োগ)](https://offschool.site/subjects/higher-math/ch08/t06/)
  - [Topic: Solution of simple trigonometric equations (সহজ ত্রিকোণমিতিক সমীকরণের সমাধান)](https://offschool.site/subjects/higher-math/ch08/t07/)
  - [Simulation: Curzon Hall clock hand and radian measure (কার্জন হলের ঘড়ির কাঁটা ও রেডিয়ান পরিমাপ)](https://offschool.site/sim/ssc.higher-math.ch08.clock-hand-radians/): The minute hand of the historic Curzon Hall clock turns 120° in 20 minutes. When the hand turns for half an hour (30 minutes) through a straight angle of 180°, how many radians is that 180° angle?
  - [Simulation: Ferris wheel reverse rotation and allied angles (নাগরদোলার উল্টো ঘূর্ণন ও সংযুক্ত কোণ)](https://offschool.site/sim/ssc.higher-math.ch08.ferris-wheel-allied-angles/): A Ferris wheel at a Boishakhi fair usually turns counter-clockwise. At an angle of 30°, a seat is above the horizontal axis and sin 30° = 0.5. But the operator suddenly turns the wheel backwards (clockwise) by 30°, so the angle is θ = −30°. Now the seat drops below the horizontal axis. What will be the value of sin(−30°)?
  - [Simulation: Swing height and trigonometric equations (দোলনার উচ্চতা ও ত্রিকোণমিতিক সমীকরণ)](https://offschool.site/sim/ssc.higher-math.ch08.swing-trig-equation/): A playground swing moves periodically so its height above the rest point is proportional to sin θ. In one full cycle from 0° to 360°, at which angles is sin θ = 1/2 (0.5)? How many solutions exist within 0° to 360°?
  - [Simulation: Unit circle and sign of sine in the third quadrant (একক বৃত্ত ও ৩য় চতুর্ভাগে সাইনের চিহ্ন)](https://offschool.site/sim/ssc.higher-math.ch08.unit-circle-sine/): A Ferris wheel of unit radius (r = 1) at a Boishakhi Mela rotates counter-clockwise about its center (0, 0). The vertical y-coordinate of a point on the rim represents sin θ. In the first quadrant at an angle of 30°, the point is above the horizontal axis, so sin 30° = +0.5. When the wheel turns into the third quadrant to 210°, what will be the sign and value of sin θ?
- [Chapter 9: Exponential and Logarithmic Function (সূচকীয় ও লগারিদমীয় ফাংশন)](https://offschool.site/subjects/higher-math/ch09/)
  - [Topic: Rational and irrational exponents (মূলদ ও অমূলদ সূচক)](https://offschool.site/subjects/higher-math/ch09/t01/)
  - [Topic: Laws of exponents (for rational and irrational exponents) (সূচক সম্পর্কিত বিভিন্ন সূত্র (মূলদ ও অমূলদ সূচকের জন্য))](https://offschool.site/subjects/higher-math/ch09/t02/)
  - [Topic: Logarithms (লগারিদম)](https://offschool.site/subjects/higher-math/ch09/t03/)
  - [Topic: Exponential, logarithmic and absolute value functions (সূচকীয়, লগারিদমীয় ও পরমমান ফাংশন)](https://offschool.site/subjects/higher-math/ch09/t04/)
  - [Topic: Graphs of the functions (ফাংশনসমূহের লেখচিত্র)](https://offschool.site/subjects/higher-math/ch09/t05/)
  - [Topic: Finding logarithms and antilogarithms with a calculator (ক্যালকুলেটরের সাহায্যে লগ ও প্রতিলগ নির্ণয়)](https://offschool.site/subjects/higher-math/ch09/t06/)
  - [Simulation: Bacteria growth in curd and logarithm (দইয়ের ব্যাকটেরিয়া বৃদ্ধি ও লগারিদম)](https://offschool.site/sim/ssc.higher-math.ch09.bacteria-growth-log/): To make curd, a starter lactic acid bacterium is added to warm milk. Under favorable conditions, it doubles at each step (generation): 2 after step 1, 4 after step 2, and 8 after step 3 (2³ = 8). How many doublings (steps) are needed for the bacteria count to exceed 1000?
  - [Simulation: Square carpet and rational exponents (বর্গাকার কার্পেট ও মূলদ সূচক)](https://offschool.site/sim/ssc.higher-math.ch09.carpet-fractional-exponent/): A square carpet of area 16 m² was bought for a room floor. Finding the side of a square requires taking the square root of its area, written in exponent notation as 16^(1/2) or 16^0.5 m. Also, a water tank's capacity scales as 16^(3/4). If the exponent is 0.5, what is the value of 16^0.5 in metres?
- [Chapter 10: Binomial Expansion (দ্বিপদী বিস্তৃতি)](https://offschool.site/subjects/higher-math/ch10/)
  - [Topic: Binomial expansion (দ্বিপদী বিস্তৃতি)](https://offschool.site/subjects/higher-math/ch10/t01/)
  - [Topic: Construction of Pascal's triangle (প্যাসকেল ত্রিভুজ গঠন)](https://offschool.site/subjects/higher-math/ch10/t02/)
  - [Topic: Binomial expansion for a general power (সাধারণ ঘাতের জন্য দ্বিপদী বিস্তৃতি)](https://offschool.site/subjects/higher-math/ch10/t03/)
  - [Topic: Values of n! and ⁿCᵣ (n! ও nCr এর মান)](https://offschool.site/subjects/higher-math/ch10/t04/)
  - [Topic: Solving mathematical problems (গাণিতিক সমস্যা সমাধান)](https://offschool.site/subjects/higher-math/ch10/t05/)
  - [Simulation: DPS Savings and Binomial Expansion (ডিপিএস সঞ্চয় ও দ্বিপদী বিস্তৃতি)](https://offschool.site/sim/ssc.higher-math.ch10.dps-interest-binomial/): A school DPS account earns 10% compound interest per year (b = 0.1). After 1 year, Tk 1 grows to Tk 1.10. Using the binomial expansion (1 + 0.1)⁵, how much will Tk 1 grow to after 5 years?
  - [Simulation: Pascal's Triangle and Binomial Expansion (প্যাসকেলের ত্রিভুজ ও দ্বিপদী বিস্তৃতি)](https://offschool.site/sim/ssc.higher-math.ch10.pascal-expansion/): An entrance arch for a science fair is decorated using Pascal's triangle. Up to (a + b)⁴, there are 5 terms and the middle coefficient is 6 (1, 4, 6, 4, 1). If the arch pattern is expanded to (a + b)⁶, how many terms will there be, and what will the middle term's coefficient be?
- [Chapter 11: Coordinate Geometry (স্থানাঙ্ক জ্যামিতি)](https://offschool.site/subjects/higher-math/ch11/)
  - [Topic: Cartesian coordinates in a plane (সমতলে কার্তেসীয় স্থানাঙ্ক)](https://offschool.site/subjects/higher-math/ch11/t01/)
  - [Topic: Distance between two points (দুইটি বিন্দুর মধ্যবর্তী দূরত্ব)](https://offschool.site/subjects/higher-math/ch11/t02/)
  - [Topic: Slope and equation of a straight line (সরলরেখার ঢাল ও সমীকরণ)](https://offschool.site/subjects/higher-math/ch11/t03/)
  - [Topic: Areas of triangles and quadrilaterals (ত্রিভুজ ও চতুর্ভুজের ক্ষেত্রফল)](https://offschool.site/subjects/higher-math/ch11/t04/)
  - [Topic: Construction of triangles and quadrilaterals (ত্রিভুজ ও চতুর্ভুজ অঙ্কন)](https://offschool.site/subjects/higher-math/ch11/t05/)
  - [Topic: Graph of a straight line (সরলরেখার লেখচিত্র)](https://offschool.site/subjects/higher-math/ch11/t06/)
  - [Simulation: Flyover ramp slope and line equation (ফ্লাইওভারের র‍্যাম্পের ঢাল ও সরলরেখার সমীকরণ)](https://offschool.site/sim/ssc.higher-math.ch11.flyover-ramp-slope/): An approach ramp is planned for the Mayor Mohammad Hanif Flyover in Dhaka. Starting from ground level at origin A(0, 0), the ramp rises 1 m for every 10 m along the road horizontally, reaching point B(10, 1). What will be the slope of this ramp, and what is its angle of inclination with the ground?
  - [Simulation: Triangular mouza plot area (মৌজা নকশায় ত্রিভুজাকার প্লটের ক্ষেত্রফল)](https://offschool.site/sim/ssc.higher-math.ch11.mouza-plot-area/): On a mouza survey map on a grid, the three boundary pegs of a triangular plot are A(1, 1), B(7, 2), and C(4, 6) (where each coordinate unit represents 10 m). What is the area of this triangular plot on the map in square units?
  - [Simulation: Bus stop between villages: Section formula (দুই গ্রামের মাঝে বাসস্টপ: রেখাংশের বিভাজন সূত্র)](https://offschool.site/sim/ssc.higher-math.ch11.section-formula/): In an upazila, village Polashpur A(2, 1) and village Anandapur B(8, 13) are connected by a straight road (coordinate units in km). Initially, a bus stop stood halfway (1:1 ratio) at the midpoint (5, 7). Due to higher population in Anandapur, the upazila decides to relocate the bus stop to point P dividing the road from Polashpur to Anandapur in a 2:1 ratio. What will be the coordinates of the new bus stop P?
- [Chapter 12: Planar Vector (সমতলীয় ভেক্টর)](https://offschool.site/subjects/higher-math/ch12/)
  - [Topic: Scalar and vector quantities (স্কেলার রাশি ও ভেক্টর রাশি)](https://offschool.site/subjects/higher-math/ch12/t01/)
  - [Topic: Equal vectors, opposite vectors and position vectors (সমান ভেক্টর, বিপরীত ভেক্টর ও অবস্থান ভেক্টর)](https://offschool.site/subjects/higher-math/ch12/t02/)
  - [Topic: Addition of vectors and the laws of addition (ভেক্টর যোগ ও যোগবিধি)](https://offschool.site/subjects/higher-math/ch12/t03/)
  - [Topic: Scalar multiples of a vector and unit vectors (ভেক্টরের স্কেলার গুণিতক ও একক ভেক্টর)](https://offschool.site/subjects/higher-math/ch12/t04/)
  - [Topic: Various geometric problems (বিভিন্ন জ্যামিতিক সমস্যা)](https://offschool.site/subjects/higher-math/ch12/t05/)
  - [Simulation: Crossing the Padma and vector addition (পদ্মা নদী পারাপার ও ভেক্টর যোগ)](https://offschool.site/sim/ssc.higher-math.ch12.boat-across-river/): In still water, a boat rows straight north at 4 m/s and lands directly opposite (current bx = 0, resultant angle 90°). Now the Padma river begins flowing east with a current of 3 m/s (bx = 3 m/s). If the boatman still rows straight north (ax = 0, ay = 4 m/s), will the boat land directly opposite, and what will its resultant speed be?
  - [Simulation: Map direction arrow and unit vector (ম্যাপের দিক নির্দেশক তীর ও একক ভেক্টর)](https://offschool.site/sim/ssc.higher-math.ch12.map-arrow-unit-vector/): A ride-sharing map app represents a car's direction of motion as vector a = (6, 8). The original vector has length |a| = √(6² + 8²) = 10. To display the arrow cleanly on the mobile screen, the app multiplies it by scalar k = 0.5 to form vector 0.5a. What will be the length of this new vector 0.5a?
  - [Simulation: Tug-of-war: equal and opposite vectors (দড়ি টানাটানি: সমান ও বিপরীত ভেক্টর)](https://offschool.site/sim/ssc.higher-math.ch12.tug-of-war-vectors/): At the school sports day tug-of-war, the first team pulls with force a = (5, 0), where ax = 5 and ay = 0. Now the second team pulls from the opposite direction with force b = (−5, 0). What will the resultant force on the rope be, and which way will the rope move?
- [Chapter 13: Solid Geometry (ঘন জ্যামিতি)](https://offschool.site/subjects/higher-math/ch13/)
  - [Topic: Basic concepts of solid geometry (ঘন জ্যামিতির মৌলিক ধারণা)](https://offschool.site/subjects/higher-math/ch13/t01/)
  - [Topic: Rectangular solids and cubes (আয়তাকার ঘনবস্তু ও ঘনক)](https://offschool.site/subjects/higher-math/ch13/t02/)
  - [Topic: Volumes and surface areas of prisms, pyramids, spheres and right circular cones (প্রিজম, পিরামিড, গোলক, ও সমবৃত্তভূমিক কোণকের আয়তন এবং পৃষ্ঠতলের ক্ষেত্রফল)](https://offschool.site/subjects/higher-math/ch13/t03/)
  - [Topic: Real-life problems on solids (ঘনবস্তু সংক্রান্ত বাস্তব সমস্যা)](https://offschool.site/subjects/higher-math/ch13/t04/)
  - [Topic: Measuring the volume and surface area of compound solids (যৌগিক ঘনবস্তুর আয়তন এবং পৃষ্ঠতলের ক্ষেত্রফল পরিমাপ)](https://offschool.site/subjects/higher-math/ch13/t05/)
  - [Simulation: Cutting a soap bar: Area vs. volume (সাবান কেটে টুকরো করা: ক্ষেত্রফল বনাম আয়তন)](https://offschool.site/sim/ssc.higher-math.ch13.cutting-a-cuboid/): A rectangular bar of soap has length 6 cm, width 4 cm, and height 3 cm. Its initial volume is 72 cm³ and total surface area is 108 cm². The soap is cut in half along its length, width, and height into 8 identical smaller pieces (2 pieces per edge). What will be the total surface area of all 8 pieces combined? Does the total volume change?
  - [Simulation: Double the tent's peak: how much more air? (তাঁবুর চূড়া দ্বিগুণ উঁচু করলে বাতাস কত বাড়ে?)](https://offschool.site/sim/ssc.higher-math.ch13.flood-shelter-tent/): For flood shelters, a relief agency builds tents as a cone on a cylinder: radius 3 m, cylinder 4 m tall, cone 4 m tall. To get more air inside, if the cone is made 8 m tall, by how much does the tent's volume grow?
  - [Simulation: Kulfi cone vs. cup: Volume and surface area (কুলফির কোণ বনাম কাপ: আয়তন ও ক্ষেত্রফল)](https://offschool.site/sim/ssc.higher-math.ch13.kulfi-cone-vs-cup/): A kulfi shop sells two containers at the same price: an ice-cream cone and a cylindrical cup. Both have base radius 3 cm and height 9 cm. How much kulfi does the cone hold compared with the cup?
  - [Simulation: Two lines that never meet but aren't parallel? (দুটি রেখা মেলে না, সমান্তরালও নয়?)](https://offschool.site/sim/ssc.higher-math.ch13.skew-lines-in-a-room/): A classroom is a cuboid ABCD-EFGH, floor ABCD and ceiling EFGH. AB is an edge of the floor and FG a side edge of the ceiling. Rafi says that two lines that never meet must be parallel. How are AB and FG related?
- [Chapter 14: Probability (সম্ভাবনা)](https://offschool.site/subjects/higher-math/ch14/)
  - [Topic: Probability and its uses (সম্ভাবনা ও এর ব্যবহার)](https://offschool.site/subjects/higher-math/ch14/t01/)
  - [Simulation: Coin Tosses: Probability vs. Relative Frequency (মুদ্রা নিক্ষেপ: সম্ভাবনা বনাম আপেক্ষিক গণসংখ্যা)](https://offschool.site/sim/ssc.higher-math.ch14.coin-tosses/): A fair coin is chosen for the cricket toss at a school sports day. The theoretical probability of getting a head (H) in a single toss is 0.5 (1/2). Abir says: 'Since the probability is 0.5, tossing it 10 times will always give exactly 5 heads.' Rafi says: 'It may not be exactly 5 in 10 tosses, but increasing tosses to 1000 will bring the relative frequency very close to 0.5.' What actually happens in 10 tosses and 1000 tosses?
  - [Simulation: Two Dice in Ludo: Which Sum Appears Most Often? (লুডুর দুই ছক্কা: কোন যোগফল সবচেয়ে বেশি আসে?)](https://offschool.site/sim/ssc.higher-math.ch14.ludo-two-dice-sum/): During a holiday afternoon game of Ludo with friends, two dice are rolled together. To advance tokens faster, players notice that adding the pips on both dice gives different totals. One player says every total from 2 to 12 is equally likely. Another claims 12 comes up most often because it is the largest. Are all totals really equally likely, or is one specific sum most likely to appear?

## ICT (তথ্য ও যোগাযোগ প্রযুক্তি)

Computer and user safety, the internet, spreadsheets, multimedia and databases, understand them by doing.

- [SSC ICT](https://offschool.site/subjects/ict/): কম্পিউটার ও ব্যবহারকারীর নিরাপত্তা, ইন্টারনেট, স্প্রেডশিট, মাল্টিমিডিয়া আর ডেটাবেজ, হাতে-কলমে করে বোঝো।
- [Chapter 1: Information and Communication Technology and Our Bangladesh (তথ্য ও যোগাযোগ প্রযুক্তি ও আমাদের বাংলাদেশ)](https://offschool.site/subjects/ict/ch01/)
  - [Topic: Twenty-First Century and Information and Communication Technology (একুশ শতক এবং তথ্য ও যোগাযোগ প্রযুক্তি)](https://offschool.site/subjects/ict/ch01/t01/)
  - [Topic: Notable Personalities in the Development of Information and Communication Technology (তথ্য ও যোগাযোগের প্রযুক্তি বিকাশে উল্লেখযোগ্য ব্যক্তিত্ব)](https://offschool.site/subjects/ict/ch01/t02/)
  - [Topic: E-learning and Bangladesh (ই-লার্নিং ও বাংলাদেশ)](https://offschool.site/subjects/ict/ch01/t03/)
  - [Topic: E-governance and Bangladesh (ই-গভর্নেন্স ও বাংলাদেশ)](https://offschool.site/subjects/ict/ch01/t04/)
  - [Topic: E-service and Bangladesh (ই-সার্ভিস ও বাংলাদেশ)](https://offschool.site/subjects/ict/ch01/t05/)
  - [Topic: E-commerce and Bangladesh (ই-কমার্স ও বাংলাদেশ)](https://offschool.site/subjects/ict/ch01/t06/)
  - [Topic: ICT in the Workplace of Bangladesh (বাংলাদেশের কর্মক্ষেত্রে আইসিটি)](https://offschool.site/subjects/ict/ch01/t07/)
  - [Topic: Social Communication and ICT (সামাজিক যোগাযোগ ও আইসিটি)](https://offschool.site/subjects/ict/ch01/t08/)
  - [Topic: Entertainment and ICT (বিনোদন ও আইসিটি)](https://offschool.site/subjects/ict/ch01/t09/)
  - [Topic: Digital Bangladesh (ডিজিটাল বাংলাদেশ)](https://offschool.site/subjects/ict/ch01/t10/)
  - [Simulation: Money transfer process in mobile banking (মোবাইল ব্যাংকিংয়ে অর্থ স্থানান্তর প্রক্রিয়া)](https://offschool.site/sim/ssc.ict.ch01.mobile-payment-trace/): Shamim, a class nine student, bought ICT reference books worth 500 BDT from a bookshop in Nilkhet. Having no cash, he decided to pay the merchant via mobile banking (such as bKash or Nagad). After entering the merchant number and amount (500 BDT), Shamim typed his secret 5-digit PIN and pressed Send. Within 3 s, both Shamim and the shopkeeper received confirmation SMS messages with a TrxID. Across the phone, server, bank, and merchant in this transaction chain, where was Shamim's secret PIN actually verified against stored data?
  - [Simulation: Does checking before sharing stop a rumour? (যাচাই করে শেয়ার করলে গুজব কি থামে?)](https://offschool.site/sim/ssc.ict.ch01.rumour-on-social-media/): A fake post is spreading on Facebook: 'All schools closed from tomorrow'. Each sharer's 6 friends see it, and about 30% of them share it again. The class decides that half of people will check an official source before sharing. What happens to the rumour?
- [Chapter 2: Computer Maintenance and Cyber Security (কম্পিউটার রক্ষণাবেক্ষণ ও সাইবার নিরাপত্তা)](https://offschool.site/subjects/ict/ch02/)
  - [Topic: Computer maintenance: preventive and corrective (কম্পিউটার রক্ষণাবেক্ষণ: প্রতিরোধমূলক ও সংশোধনমূলক)](https://offschool.site/subjects/ict/ch02/t10/)
  - [Topic: Importance of software in computer maintenance (কম্পিউটার রক্ষণাবেক্ষণে সফটওয়্যারের গুরুত্ব)](https://offschool.site/subjects/ict/ch02/t01/)
  - [Topic: Installing, uninstalling and deleting software (সফটওয়্যার ইনস্টলেশন ও আনইনস্টলেশন এবং ডিলিট)](https://offschool.site/subjects/ict/ch02/t02/)
  - [Topic: Information security and cyber risk (তথ্যের নিরাপত্তা ও সাইবার ঝুঁকি)](https://offschool.site/subjects/ict/ch02/t11/)
  - [Topic: Cyber crime (সাইবার অপরাধ)](https://offschool.site/subjects/ict/ch02/t12/)
  - [Topic: Security strategies for the Internet (ইন্টারনেট ব্যবহারের নিরাপত্তা কৌশল)](https://offschool.site/subjects/ict/ch02/t03/)
  - [Topic: Staying safe on the web (ওয়েবে নিরাপদ থাকা)](https://offschool.site/subjects/ict/ch02/t04/)
  - [Topic: Addiction to the Internet, computer games and social networking sites (ইন্টারনেট, কম্পিউটার গেম ও সামাজিক নেটওয়ার্কে আসক্তি)](https://offschool.site/subjects/ict/ch02/t05/)
  - [Topic: The way out of addiction (আসক্তি থেকে মুক্তি)](https://offschool.site/subjects/ict/ch02/t06/)
  - [Topic: Piracy (পাইরেসি)](https://offschool.site/subjects/ict/ch02/t07/)
  - [Topic: Right to information and security (তথ্য অধিকার ও নিরাপত্তা)](https://offschool.site/subjects/ict/ch02/t08/)
  - [Topic: General troubleshooting (সাধারণ ট্রাবল শ্যুটিং)](https://offschool.site/subjects/ict/ch02/t09/)
  - [Simulation: The computer won't start: what first? (কম্পিউটার চালু হচ্ছে না: আগে কী দেখবে?)](https://offschool.site/sim/ssc.ict.ch02.computer-wont-start/): The morning after a storm, one computer in the school lab won't switch on; not a single light comes on. Someone says the motherboard has burnt out and a new computer is needed. What should be checked first?
  - [Simulation: Is the bKash bonus link safe? (বিকাশ বোনাসের লিংকটি কি নিরাপদ?)](https://offschool.site/sim/ssc.ict.ch02.is-this-link-safe/): A message arrives on Mother's phone: 'Congratulations! You have won a 5000 Tk bonus, click here now and enter your PIN: http://free-gift-bkash.xyz/win'. Is the link safe?
  - [Simulation: Password strength: length vs special symbols (পাসওয়ার্ডের শক্তিমত্তা: দৈর্ঘ্য বনাম বিশেষ চিহ্ন)](https://offschool.site/sim/ssc.ict.ch02.password-strength/): Adnan created an 8-character password using only lowercase letters (a–z, 26 characters). An attacker using a powerful GPU tests 10 billion (10¹⁰) guesses per second, cracking it in just 10.4 seconds on average. Adnan wants to make it much stronger. He is deciding between adding 32 special symbols to the 8-character password, or keeping only lowercase letters but increasing the length to 12. Which makes the password far more secure?
  - [Simulation: With key 1, what does the secret message look like? (চাবি ১ হলে গোপন বার্তা কেমন?)](https://offschool.site/sim/ssc.ict.ch02.secret-message-cipher/): Two friends write letters in a Caesar cipher: each letter moves forward in the alphabet by the key. With key 3, MEET AT FIVE becomes PHHW DW ILYH. With key 1, what does MEET AT FIVE become?
  - [Simulation: Does deleting the icon delete the game? (আইকন মুছলে কি গেমটা মুছে যায়?)](https://offschool.site/sim/ssc.ict.ch02.uninstall-not-delete/): His laptop running out of space, Rafi deletes the desktop icon of an 800 MB game. He thinks the game is now gone and the space is free. How much space has been freed?
- [Chapter 3: Internet and Introduction to Web (ইন্টারনেট ও ওয়েব পরিচিতি)](https://offschool.site/subjects/ict/ch03/)
  - [Topic: Digital content and its types (ডিজিটাল কনটেন্ট ও এর প্রকারভেদ)](https://offschool.site/subjects/ict/ch03/t01/)
  - [Topic: Internet in education (শিক্ষায় ইন্টারনেট)](https://offschool.site/subjects/ict/ch03/t02/)
  - [Topic: The Internet and my school subjects (ইন্টারনেট ও আমার পাঠ্য বিষয়গুলো)](https://offschool.site/subjects/ict/ch03/t03/)
  - [Topic: My future career and ICT (আমার ভবিষ্যৎ ক্যারিয়ার ও আইসিটি)](https://offschool.site/subjects/ict/ch03/t04/)
  - [Topic: Web page, website and web portal (ওয়েব পেইজ, ওয়েবসাইট ও ওয়েব পোর্টাল)](https://offschool.site/subjects/ict/ch03/t05/)
  - [Topic: Web server and web client (ওয়েব সার্ভার ও ওয়েব ক্লায়েন্ট)](https://offschool.site/subjects/ict/ch03/t06/)
  - [Topic: Web browser (ওয়েব ব্রাউজার)](https://offschool.site/subjects/ict/ch03/t07/)
  - [Simulation: Packet Routing and Alternative Paths (ইন্টারনেটে প্যাকেট রাউটিং ও বিকল্প পথ)](https://offschool.site/sim/ssc.ict.ch03.packet-routing/): A digital textbook download request is sent from a school lab to the central NCTB e-book server. The delay from lab to local router is 5 ms, and normally the request travels via direct optical fiber across two links (15 ms each), taking 35 ms in total.

Road excavation cuts the primary optical fiber cable. Routers automatically redirect packets along an alternative regional path of 3 links with 20 ms delay each. How much total delay (in ms) will it take for the request to reach the server via the alternative path?
- [Chapter 4: My Writing and Accounts (আমার লেখালেখি ও হিসাব)](https://offschool.site/subjects/ict/ch04/)
  - [Topic: My writing work in a word processor (ওয়ার্ড প্রসেসরে আমার লেখার কাজ)](https://offschool.site/subjects/ict/ch04/t01/)
  - [Topic: Spreadsheets and my accounts (স্প্রেডসিট ও আমার হিসাব নিকাশ)](https://offschool.site/subjects/ict/ch04/t02/)
  - [Simulation: Spreadsheet functions and class average (স্প্রেডশিট ফাংশন ও শ্রেণির গড় নম্বর)](https://offschool.site/sim/ssc.ict.ch04.class-average-spreadsheet/): The class monitor stored five friends' ICT exam marks in spreadsheet cells B1 to B5: 70 in B1, 50 in B2, 80 in B3, 40 in B4, and 60 in B5. Their average was 60 (total 300). However, the fifth student was actually absent, so their mark should be 0 instead of 60. If cell B5 is changed to 0, what will the formula =AVERAGE(B1:B5) show for the class average?
  - [Simulation: Spreadsheet marksheet and relative cell references (স্প্রেডশিটে ফলাফল ও সূত্রের আপেক্ষিক রেফারেন্স)](https://offschool.site/sim/ssc.ict.ch04.marksheet-formula/): A class 9 ICT teacher recorded five students' marks in spreadsheet cells B1 to B5: 78 in B1, 45 in B2, 30 in B3, 88 in B4, and 60 in B5. The pass mark is 33.
To evaluate the first student, he entered the formula in cell C1: =IF(B1>=33,"Pass","Fail").
He then dragged the fill handle down one row into cell C2 for the second student. What formula appears in cell C2?
- [Chapter 5: Multimedia and Graphics (মাল্টিমিডিয়া ও গ্রাফিক্স)](https://offschool.site/subjects/ict/ch05/)
  - [Topic: Concept of multimedia (মাল্টিমিডিয়ার ধারণা)](https://offschool.site/subjects/ict/ch05/t01/)
  - [Topic: Media of multimedia (মাল্টিমিডিয়ার মাধ্যমসমূহ)](https://offschool.site/subjects/ict/ch05/t02/)
  - [Topic: Use of multimedia in information and communication technology (তথ্য ও যোগাযোগ প্রযুক্তিতে মাল্টিমিডিয়ার ব্যবহার)](https://offschool.site/subjects/ict/ch05/t03/)
  - [Topic: Presentation software (প্রেজেন্টেশন সফটওয়্যার)](https://offschool.site/subjects/ict/ch05/t04/)
  - [Topic: Concept of graphics (গ্রাফিক্স এর ধারণা)](https://offschool.site/subjects/ict/ch05/t05/)
  - [Topic: Techniques of using graphics software (গ্রাফিক্স সফটওয়্যার ব্যবহার কৌশল)](https://offschool.site/subjects/ict/ch05/t06/)
  - [Simulation: Why does the logo break up when enlarged? (লোগো বড় করলে কেন ভেঙে যায়?)](https://offschool.site/sim/ssc.ict.ch05.logo-on-a-banner/): For the school's annual function banner, the 400-pixel-wide school logo picture (a JPG) is to be enlarged four times. The teacher says a vector file would have been better. Enlarged to 400%, how will the JPG logo look?
  - [Simulation: Image resolution and file size: what happens when dimensions double? (ছবির রেজোলিউশন ও ফাইলের আকার: মাত্রা দ্বিগুণ হলে কী ঘটে?)](https://offschool.site/sim/ssc.ict.ch05.photo-file-size/): Rafi took a photo on a digital camera for his school science fair. The image has a width of 1024 pixels, a height of 1024 pixels, and a colour depth of 24 bits (True Colour). In computer memory, its uncompressed file size is 3 MB. If Rafi doubles both the width and height to 2048 × 2048 pixels, what will the new file size be?
  - [Simulation: Science fair video size: what happens when frame rate doubles? (বিজ্ঞান মেলার ভিডিওর আকার: ফ্রেম রেট দ্বিগুণ হলে কী ঘটে?)](https://offschool.site/sim/ssc.ict.ch05.science-fair-video-size/): Rafi recorded a 1-minute Full HD video for his school science fair. The video resolution is 1920 × 1080 pixels per frame, colour depth is 24-bit True Colour, and the frame rate is 30 frames per second (30 fps). In computer memory, its uncompressed file size is about 10.4 GB. If Rafi doubles the frame rate to 60 fps, what will the video file size be?
- [Chapter 6: Problem Solving through Programming (প্রোগ্রামিংয়ের মাধ্যমে সমস্যার সমাধান)](https://offschool.site/subjects/ict/ch06/)
  - [Topic: Problem solving, programming languages, machine code, compiler and interpreter (সমস্যা সমাধান, প্রোগ্রামিং ভাষা, মেশিন কোড, কম্পাইলার ও ইন্টারপ্রেটার)](https://offschool.site/subjects/ict/ch06/t01/)
  - [Topic: Starting the journey of programming in Python (পাইথনে প্রোগ্রামিংয়ের যাত্রা শুরু)](https://offschool.site/subjects/ict/ch06/t02/)
  - [Topic: Showing text, variables and naming (টেক্সট প্রদর্শন, ভ্যারিয়েবল ও নামকরণ)](https://offschool.site/subjects/ict/ch06/t03/)
  - [Topic: Data types and type casting (ডেটাটাইপ ও টাইপ কাস্টিং)](https://offschool.site/subjects/ict/ch06/t04/)
  - [Topic: Taking input and arithmetic operations (ইনপুট গ্রহণ ও গাণিতিক অপারেশন)](https://offschool.site/subjects/ict/ch06/t05/)
  - [Topic: Comparison operators and conditions: if, if...else, elif (তুলনামূলক অপারেটর ও শর্ত: if, if...else, elif)](https://offschool.site/subjects/ict/ch06/t06/)
  - [Topic: The match statement (match স্টেটমেন্ট)](https://offschool.site/subjects/ict/ch06/t07/)
  - [Topic: Loops: for, nested for, while, nested while (লুপ: for, নেস্টেড for, while, নেস্টেড while)](https://offschool.site/subjects/ict/ch06/t08/)
  - [Topic: break and continue statements (break ও continue স্টেটমেন্ট)](https://offschool.site/subjects/ict/ch06/t09/)
  - [Simulation: Why 5 plus 3 gives 53: input() and type casting (৫ আর ৩ যোগ করলে ৫৩ কেন: input() ও টাইপ কাস্টিং)](https://offschool.site/sim/ssc.ict.ch06.five-plus-three/): Mitu wrote a program to add two numbers: a = input(), b = input(), then print(a + b). She ran it and typed 5, then 3. What will the screen show?
  - [Simulation: if-elif-else: which condition to check first (if-elif-else: কোন শর্ত আগে লিখবে)](https://offschool.site/sim/ssc.ict.ch06.grade-ladder-elif/): Sumaiya wrote a result program. First: if marks >= 33: print("Pass"), then elif marks >= 80: print("A+"), and finally else: print("Fail"). Her friend Ria scored 85. What will the program print?
  - [Simulation: The match statement: which day is a holiday (match স্টেটমেন্ট: কোন দিন ছুটি)](https://offschool.site/sim/ssc.ict.ch06.holiday-match/): Rafi wrote a program that looks at a day's name and says whether school is open. Under match day:, case "Fri" | "Sat" prints Holiday, case "Sun" | "Mon" | "Tue" | "Wed" | "Thu" prints School day, and case _ prints Not a day. If day = "Funday" by mistake, what is printed?
  - [Simulation: Interpreter vs compiler: what happens at a wrong line (ইন্টারপ্রেটার বনাম কম্পাইলার: ভুল লাইনে কী হয়)](https://offschool.site/sim/ssc.ict.ch06.interpreter-stops-at-error/): Tanim wrote a four-line program in Thonny. Lines 1 and 2 print A and B, line 3 prints a variable c that was never created, and line 4 prints D. Python runs through an interpreter. What will the screen show when he runs it?
  - [Simulation: for loops and range(): why adding 1 to 10 gave 45 (for লুপ ও range(): ১ থেকে ১০ যোগ করতে গিয়ে ৪৫ কেন)](https://offschool.site/sim/ssc.ict.ch06.loop-sum-range/): Rakib wanted the sum of 1 to 10 and wrote: total = 0, then for i in range(1, 10): total = total + i, and finally print(total). What will the program print?
  - [Simulation: while loops: saving in a clay piggy bank (while লুপ: মাটির ব্যাংকে টাকা জমানো)](https://offschool.site/sim/ssc.ict.ch06.piggy-bank-while/): Nusrat puts 30 taka a day into her clay piggy bank to buy a 100 taka book. She wrote: taka = 0, day = 0, while taka < 100: with taka = taka + 30 and day = day + 1 inside, then print(day, taka). What will it print?
  - [Simulation: break vs continue: stop the loop or skip one pass (break বনাম continue: লুপ থামানো নাকি একবার বাদ দেওয়া)](https://offschool.site/sim/ssc.ict.ch06.skip-or-stop/): Lima wants to print 1 to 7 but leave out multiples of 3. She wrote: for i in range(1, 8): with if i % 3 == 0: break inside, then print(i, end=" "). What appears on the screen?
  - [Simulation: Nested for loops: a triangle of stars (নেস্টেড for লুপ: তারার ত্রিভুজ)](https://offschool.site/sim/ssc.ict.ch06.star-triangle-nested/): Joy draws a triangle of stars with nested loops: for i in range(1, rows + 1): containing for j in range(1, i + 1): print("*", end=""), and print() after the inner loop. With rows = 4, how many stars are printed in all?