Assertion-Reason Questions Class 10 Science: Chapter-Wise with Answers
Assertion-reason questions for all 13 chapters of CBSE Class 10 Science, from chemical reactions to our environment, with answers and solving tips.
In an assertion-reason question you judge two statements, an Assertion (A) and a Reason (R). Decide if each is true, then whether R correctly explains A. Pick (a) both true and R explains A, (b) both true but R does not explain A, (c) A true, R false, or (d) A false, R true. Chapter-wise Class 10 Science practice questions with answers follow.
Assertion-reason questions appear in CBSE Class 10 Science papers every year because they test whether you understand why something happens, not just what happens. This page gives you the solving method and chapter-wise assertion-reason questions for all 13 chapters of Class 10 Science, with answers and explanations. All questions are original, written by the Intellicamp team, and follow the current rationalised NCERT syllabus.
How to solve assertion-reason questions
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
- Read A on its own. True or false?
- Read R on its own. True or false?
- If both are true, ask "Is R the reason A happens?" Yes means (a); no means (b).
Shortcut: A false means (d); A true with R false means (c).
Chapter 1: Chemical Reactions and Equations
Q1. A: When a magnesium ribbon burns in air, a white powder is formed.
R: Magnesium combines with oxygen to form magnesium oxide.
Show answer
(a). The white powder is magnesium oxide: 2Mg + O₂ → 2MgO.
Q2. A: Respiration is an exothermic process.
R: During respiration, glucose combines with oxygen in our cells and releases energy.
Show answer
(a). Releasing energy is what makes a reaction exothermic.
Q3. A: Fe + CuSO₄ → FeSO₄ + Cu is a decomposition reaction.
R: In a displacement reaction, a more reactive element displaces a less reactive element from its compound.
Show answer
(d). Iron displaces copper, so it is a displacement reaction, not decomposition. R is true.
Chapter 2: Acids, Bases and Salts
Q1. A: Sodium hydrogencarbonate is used as an ingredient in antacids.
R: Being alkaline, it neutralises excess acid in the stomach.
Show answer
(a). Neutralising extra stomach acid is exactly how an antacid gives relief.
Q2. A: A solution with pH 3 is more acidic than a solution with pH 5.
R: The lower the pH, the higher the concentration of hydrogen ions.
Show answer
(a). More hydrogen ions means a stronger acidic solution.
Q3. A: Distilled water is a good conductor of electricity.
R: Acids and bases conduct electricity in water because they produce ions.
Show answer
(d). Distilled water has almost no ions, so it conducts very poorly. R is true.
Chapter 3: Metals and Non-metals
Q1. A: Aluminium is used to make cooking utensils.
R: Aluminium is a good conductor of heat.
Show answer
(a). Good heat conduction cooks food evenly; aluminium is also light and resists corrosion.
Q2. A: Sodium is stored under kerosene.
R: Sodium reacts vigorously with oxygen and moisture in the air.
Show answer
(a). Kerosene keeps air and moisture away and prevents sodium catching fire.
Q3. A: Copper displaces zinc from zinc sulphate solution.
R: Zinc is more reactive than copper.
Show answer
(d). A less reactive metal (copper) cannot displace a more reactive one (zinc). R is true.
Chapter 4: Carbon and its Compounds
Q1. A: Carbon mostly forms covalent bonds.
R: Carbon cannot easily gain or lose four electrons, so it shares electrons instead.
Show answer
(a). Sharing electrons is what a covalent bond is.
Q2. A: Ethanol and ethanoic acid can be told apart using sodium hydrogencarbonate.
R: Ethanoic acid reacts with sodium hydrogencarbonate to release carbon dioxide, but ethanol does not.
Show answer
(a). Brisk effervescence appears only with the acid.
Q3. A: Soaps form a scum with hard water.
R: Detergents form insoluble salts with the calcium and magnesium ions in hard water.
Show answer
(c). A is true. R is false: it is soaps, not detergents, that form insoluble scum; detergents still lather in hard water.
Chapter 5: Life Processes
Q1. A: Arteries have thick, elastic walls.
R: Arteries carry blood away from the heart under high pressure.
Show answer
(a). Thick, elastic walls withstand and smooth out the high pressure.
Q2. A: The inner wall of the small intestine has many finger-like projections called villi.
R: Villi increase the surface area for absorption of digested food.
Show answer
(a). The larger surface area is why villi are there.
Q3. A: Green plants release oxygen only at night.
R: Oxygen is released during photosynthesis, which needs light.
Show answer
(d). R shows oxygen is released in light, during the day, so A is false.
Chapter 6: Control and Coordination
Q1. A: You pull your hand away from a hot object before you feel the pain.
R: Reflex actions are controlled by the spinal cord, without waiting for the brain to think.
Show answer
(a). The reflex arc through the spinal cord is faster than the signal reaching the brain.
Q2. A: A lack of insulin can cause diabetes.
R: Insulin helps regulate the level of sugar in the blood.
Show answer
(a). Without enough insulin, blood sugar rises, which is diabetes.
Q3. A: The shoot of a plant bends towards light.
R: Light makes auxin move to the lit side of the shoot, so that side grows faster.
Show answer
(c). A is true. R is false: auxin moves to the shaded side, which then grows faster and bends the shoot towards light.
Chapter 7: How do Organisms Reproduce?
Q1. A: Offspring from asexual reproduction are very similar to the parent.
R: Asexual reproduction involves only one parent.
Show answer
(a). With a single parent, the DNA is copied with very few changes, so offspring are near-copies.
Q2. A: Bryophyllum can grow new plants from its leaves.
R: Buds in the notches along the leaf margin can develop into new plants.
Show answer
(a). This is vegetative propagation through leaf buds.
Q3. A: Amoeba reproduces by budding.
R: In binary fission, a single cell divides into two daughter cells.
Show answer
(d). Amoeba reproduces by binary fission; budding is seen in Hydra and yeast. R is true.
Chapter 8: Heredity
Q1. A: In humans, the sex of a child is decided by the chromosome inherited from the father.
R: A father can pass on either an X or a Y chromosome, while a mother passes on only an X.
Show answer
(a). X from the father gives a girl (XX); Y gives a boy (XY).
Q2. A: Crossing pure tall (TT) and pure short (tt) pea plants gives only tall plants in F1.
R: Tallness is the dominant trait.
Show answer
(a). All F1 plants are Tt, and the dominant T shows as tall.
Q3. A: In the F2 generation of this cross, tall and short plants appear in the ratio 1 : 3.
R: Traits are inherited through genes from both parents.
Show answer
(d). The F2 ratio is 3 tall : 1 short. R is true.
Chapter 9: Light: Reflection and Refraction
Q1. A: A concave mirror is used as a shaving mirror.
R: A concave mirror forms an enlarged, erect image when the face is between the pole and the focus.
Show answer
(a). The enlarged, upright image is what makes it useful for shaving.
Q2. A: Convex mirrors are used as rear-view mirrors in vehicles.
R: A convex mirror always forms an erect, diminished image and gives a wide field of view.
Show answer
(a). The driver sees more of the road behind, the right way up.
Q3. A: The refractive index of glass is 1.5, so light travels faster in glass than in air.
R: Refractive index = speed of light in vacuum ÷ speed of light in the medium.
Show answer
(d). From R, a refractive index of 1.5 means light is 1.5 times slower in glass. A is false.
Q4. A: A convex lens of focal length 50 cm has a power of +2 D.
R: The power of a lens is P = 1/f, where f is in centimetres.
Show answer
(c). P = 1/0.5 m = +2 D, so A is true. R is false: f must be in metres.
Chapter 10: The Human Eye and the Colourful World
Q1. A: The clear sky looks blue.
R: Very small particles in the atmosphere scatter blue light much more than red light.
Show answer
(a). Scattered blue light reaches our eyes from all directions.
Q2. A: A person with myopia sees distant objects clearly.
R: Myopia is corrected with a concave lens.
Show answer
(d). Myopia is near-sightedness: distant objects look blurred. R is true.
Q3. A: Stars twinkle.
R: Starlight is continuously refracted by layers of air whose conditions keep changing.
Show answer
(a). The changing refraction makes the star's brightness and position flicker.
Q4. A: Danger signal lights are red.
R: Red light is scattered the most by fog and smoke.
Show answer
(c). A is true. R is false: red light is scattered the least, so it travels farthest through fog and smoke.
Chapter 11: Electricity
Q1. A: Resistors of 4 Ω and 6 Ω in series have a total resistance of 10 Ω.
R: In a series combination, the total resistance is the sum of the individual resistances.
Show answer
(a). 4 + 6 = 10 Ω.
Q2. A: Household appliances are connected in parallel.
R: In parallel, each appliance gets the full mains voltage and can be switched on or off independently.
Show answer
(a). These two advantages are why homes use parallel wiring.
Q3. A: Copper is used for electric transmission wires.
R: Copper has a very high resistivity.
Show answer
(c). A is true. R is false: copper has a very low resistivity, which is why it is used.
Chapter 12: Magnetic Effects of Electric Current
Q1. A: Two magnetic field lines never intersect.
R: If they did, the field would have two directions at the same point, which is impossible.
Show answer
(a). The field has one direction at each point.
Q2. A: The magnetic field inside a long current-carrying solenoid is nearly uniform.
R: Inside the solenoid, the field lines are parallel straight lines.
Show answer
(a). Parallel, evenly spaced lines mean a uniform field.
Q3. A: An electric fuse is connected in parallel with the appliance it protects.
R: A fuse melts and breaks the circuit when too much current flows.
Show answer
(d). A fuse must be in series, or it could not break the circuit. R is true.
Chapter 13: Our Environment
Q1. A: Depletion of the ozone layer is harmful to life on Earth.
R: The ozone layer absorbs most of the harmful ultraviolet radiation from the sun.
Show answer
(a). Less ozone lets more UV radiation reach the surface.
Q2. A: Only about 10% of the energy at one trophic level passes to the next.
R: Much of the energy at each level is used for life processes or lost as heat.
Show answer
(a). That loss is why food chains rarely have more than four or five levels.
Q3. A: Plastic bags are biodegradable.
R: Biodegradable substances are broken down by microorganisms.
Show answer
(d). Plastic bags are not broken down by microorganisms, so they are non-biodegradable. R is true.
How to practise these well
- Link to the NCERT text: most reasons come straight from a line or activity in the NCERT Science textbook. Find it.
- Learn the "why": for every (a), you should be able to explain the reason in your own words.
- Practise more: the NCERT Exemplar problems and CBSE's 2025-26 sample papers have more questions in this style.
Next, try our chapter-wise MCQs for Class 10 Science or the Maths assertion-reason set. For the newer case-based style, read about competency-based questions. On Intellicamp, chapter-wise Science tests mix every question type, are marked instantly, and show your weakest topics. See how it works for students.
- Judge A, then R, then whether R explains A.
- Most reasons come from NCERT explanations, so read the "why" behind each fact.
- Practise all 13 chapters and revisit every mistake.
Frequently asked questions
Which chapters of Class 10 Science are covered?
All 13 chapters of the current rationalised NCERT Science textbook, from Chemical Reactions and Equations to Our Environment.
Are assertion-reason questions difficult?
They test understanding rather than memory, so they feel harder at first. With the three-step method on this page, most students answer them in under a minute.
How do I decide between option (a) and (b)?
Ask whether R tells you why A is true. If R is a true statement about the same topic but does not explain A, the answer is (b).
Do these questions follow the CBSE pattern?
Yes, they use CBSE's standard four options. Check the latest sample paper on cbseacademic.nic.in to see how many appear in your paper.
Where can I take a chapter-wise Science test online?
On Intellicamp you can take chapter-wise Class 10 Science tests that include assertion-reason, MCQs and case-based questions, marked instantly with your weak topics shown.
Practise this chapter free
Take a short practice test on any chapter, get it marked instantly, and see exactly which topics are costing you marks.