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Class 10 Science important questions chapter-wise 2026-27, with marks and answers

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This page has two important questions for each of the 13 chapters of the NCERT Class 10 Science book (Reprint 2026-27): one 1-mark question, then a 3-mark or 5-mark question, labelled the way the board paper labels them. Every answer is worked out and names the textbook page it rests on, and each chapter links to a longer set of 8 practice questions.

These questions are our own, drafted with AI help. Every number and equation was re-computed by a script and every answer was checked against the NCERT chapter, but no practising teacher has reviewed them yet. None of them is a textbook exercise or a sample-paper question with the numbers changed. If you find a mistake, please tell us.

Before you start: what the 2026-27 paper examines

Chapter 1: Chemical Reactions and Equations

Q1 (1 mark, multiple choice). Which of these is a decomposition reaction? (A) CaO + H₂O → Ca(OH)₂ (B) CaCO₃ → CaO + CO₂, on heating (C) Fe + CuSO₄ → FeSO₄ + Cu (D) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Answer: (B). One reactant, limestone, breaks into two simpler products, quick lime and carbon dioxide; done by heating, it is a thermal decomposition (page 8). (A) is a combination, (C) a displacement and (D) a double displacement.

Q2 (3 marks, short answer). Cooking gas (LPG) contains propane, C₃H₈. (a) Balance the equation for burning propane: C₃H₈ + O₂ → CO₂ + H₂O. (b) Is this reaction exothermic or endothermic? (c) Which substance is oxidised?

Answer: (a) C₃H₈ + 5O₂ → 3CO₂ + 4H₂O; (b) exothermic; (c) propane. (a) Carbon: 3 on each side. Hydrogen: 8 on the left, so 4 molecules of water on the right. Oxygen: 3 × 2 + 4 × 1 = 10 atoms on the right, so 5 molecules of O₂ on the left. Only the numbers in front of the formulae change (balancing, pages 3-5). (b) Burning a fuel gives out heat, like the burning of natural gas, which the chapter lists as exothermic (page 7). (c) Propane gains oxygen: its carbon ends up in CO₂ and its hydrogen in H₂O, and a substance that gains oxygen is oxidised (page 12).

Eight more on this chapter: Chemical Reactions and Equations questions with answers.

Chapter 2: Acids, Bases and Salts

Q3 (1 mark, assertion and reason). Assertion (A): Washing soda can be made starting from baking soda. Reason (R): Heating baking soda gives sodium carbonate, and recrystallising sodium carbonate gives washing soda. (A) A and R are both true; R explains A. (B) A and R are both true; R does not explain A. (C) Only A is true. (D) Only R is true.

Answer: (A). The chapter shows both steps: heating sodium hydrogencarbonate gives sodium carbonate, and recrystallisation of sodium carbonate gives washing soda, Na₂CO₃·10H₂O (page 31).

Q4 (3 marks, short answer). A student tests three liquids from home (made-up results). X turns blue litmus red and has pH 3. Y changes neither litmus and has pH 7. Z turns red litmus blue and has pH 9. (a) Is each acidic, neutral or basic? (b) Is X more or less acidic than a liquid of pH 5? (c) Someone is stung by a honey-bee. Which kind of liquid, X or Z, would help, and what reaction is involved?

Answer: (a) X acidic, Y neutral, Z basic; (b) more acidic; (c) a mild base like Z, by neutralisation. (a) Acids turn blue litmus red and bases turn red litmus blue (page 17); on the pH scale, 7 is neutral, below 7 acidic and above 7 basic (page 25). (b) A lower pH means a higher hydronium ion concentration, so pH 3 is more acidic than pH 5 (page 25). (c) A bee-sting leaves an acid, and a mild base such as baking soda on the spot gives relief (page 28). An acid and a base react to give a salt and water: a neutralisation reaction (page 21).

Eight more: Acids, Bases and Salts questions with answers.

Chapter 3: Metals and Non-metals

Q5 (1 mark, multiple choice). Which metal reacts so violently with cold water that the hydrogen given off catches fire? (A) calcium (B) potassium (C) magnesium (D) iron

Answer: (B). Potassium and sodium react with cold water so strongly that the hydrogen catches fire. Calcium reacts less violently, and the heat is not enough to set the hydrogen alight (page 43).

Q6 (3 marks, short answer). Three metals come from three kinds of ore: mercury from cinnabar (HgS), zinc from its oxide, and sodium from its chloride. For each, say how the metal is obtained and why that method suits it.

Answer: mercury by heating alone, zinc by reducing the oxide with carbon, sodium by electrolysis of the molten chloride. Mercury is low in the activity series: heating cinnabar in air gives mercuric oxide, and further heating gives mercury, 2HgS + 3O₂ → 2HgO + 2SO₂ then 2HgO → 2Hg + O₂ (page 51). Zinc is in the middle of the series: its oxide can be reduced to the metal with carbon (page 51). Sodium is near the top: it holds oxygen more strongly than carbon does, so carbon cannot reduce it, and it is obtained by electrolysis of its molten chloride, with the metal collecting at the cathode (page 52).

Eight more: Metals and Non-metals questions with answers. Revision notes: Metals and Non-metals notes.

Chapter 4: Carbon and its Compounds

Q7 (1 mark, multiple choice). Ethanol is C₂H₅OH. The member of the same homologous series with four carbon atoms is (A) C₄H₁₀ (B) C₄H₉OH (C) C₄H₈OH (D) C₄H₁₁OH

Answer: (B). Each member of a homologous series differs from the next by a –CH₂– unit (page 66), so two steps up from C₂H₅OH is C₄H₉OH. C₄H₁₀ has no –OH group, and the other two do not fit the pattern.

Q8 (3 marks, short answer). A carpenter cleans a varnished table with denatured spirit, which is mostly ethanol. (a) What is added to ethanol to make it denatured, and why? (b) A tiny piece of sodium is dropped into pure ethanol. Write the balanced equation and name both products.

Answer: (a) a poison such as methanol, and a blue dye, so that it is not drunk; (b) 2Na + 2CH₃CH₂OH → 2CH₃CH₂O⁻Na⁺ + H₂, giving sodium ethoxide and hydrogen. (a) To stop industrial alcohol being misused for drinking, poisonous substances like methanol are mixed in, and dyes colour it blue so it is easy to recognise (page 72). (b) Sodium reacting with an alcohol releases hydrogen gas, and in ethanol's case sodium ethoxide forms as well (page 72). Check the atoms: 2 Na, 4 C, 12 H and 2 O on each side.

Eight more: Carbon and its Compounds questions with answers.

Chapter 5: Life Processes

Q9 (1 mark, multiple choice). Oxygen-rich blood coming back from the lungs first enters the heart's (A) right atrium (B) right ventricle (C) left atrium (D) left ventricle

Answer: (C). Blood from the lungs comes into the thin-walled upper chamber on the left, the left atrium (page 92).

Q10 (5 marks, long answer). Two potted plants of the same kind are watered equally. Plant A stands in a sunny, breezy spot; plant B stands in a humid, shaded corner. (a) During the day, which plant pulls up more water from its roots, and what causes the pull? (b) At night, which force matters more for moving water up? (c) Name the tissue that carries water and minerals, and the one that carries food. (d) A gardener removes a complete ring of bark, including the food-carrying tissue, from a branch. Predict what happens to the movement of food made in the leaves above the ring. (e) Is moving food in a plant a purely physical process like water transport? Explain.

Answer: (a) plant A, by transpiration pull; (b) root pressure; (c) xylem and phloem; (d) food cannot move past the ring; (e) no, it uses energy from ATP. (a) Water evaporating from the leaves through the stomata creates a suction that pulls water up from the roots; this loss of water vapour is transpiration (page 95). Sun and moving air dry the leaves faster, so plant A loses, and pulls up, more water than plant B. (b) Root pressure matters more at night, while in daylight, with the stomata open, transpiration pull takes over as the main force (page 95). (c) Xylem moves water and minerals from the soil; phloem carries the products of photosynthesis from the leaves to other parts (page 94). (d) Food moves in the phloem, both up and down (page 95), so with the phloem cut all round the branch, food made above the ring has no path to the parts below it. (e) No. Unlike transport in xylem, which simple physical forces largely explain, material such as sucrose is moved into the phloem using energy from ATP (page 96).

Eight more: Life Processes questions with answers. Revision notes: Life Processes notes.

Chapter 6: Control and Coordination

Q11 (1 mark, assertion and reason). Assertion (A): When your fingers touch a very hot pan, your hand pulls away before you have thought about it. Reason (R): For such a reflex, the nerve bringing the signal in is linked to the nerve carrying the order out in the spinal cord. (A) A and R are both true; R explains A. (B) A and R are both true; R does not explain A. (C) Only A is true. (D) Only R is true.

Answer: (A). A reflex is a quick action we take without thinking about it (page 102). The reflex arc is formed in the spinal cord, where nerves from the body meet on their way to the brain, so the response does not wait for the brain (pages 102-103).

Q12 (3 marks, short answer). After a sweet lunch, the sugar level in Meena's blood rises. (a) Which gland detects this, and which hormone does it release more of? (b) What is this way of keeping a hormone at the right level called? (c) Name the hormones behind the body changes of puberty in boys and in girls.

Answer: (a) the pancreas, insulin; (b) a feedback mechanism; (c) testosterone and oestrogen. (a) Pancreas cells sense the higher blood sugar and release extra insulin, the hormone that keeps blood sugar in check (pages 110-111). (b) The timing and amount of a hormone are regulated by feedback mechanisms; as blood sugar falls again, less insulin is released (page 111). (c) Boys' puberty changes are driven by testosterone, and girls' by oestrogen (page 110).

Eight more: Control and Coordination questions with answers.

Chapter 7: How do Organisms Reproduce?

Q13 (1 mark, multiple choice). A Planaria cut into several pieces gives several complete worms. This is called (A) budding (B) spore formation (C) regeneration (D) binary fission

Answer: (C). In simple animals like Hydra and Planaria, every cut piece can grow back into a whole animal; the chapter calls this regeneration (page 116).

Q14 (3 marks, short answer). A pollen grain from a mango flower lands on the stigma of another mango flower. (a) How does the male germ-cell reach the egg? (b) What is formed when they fuse, and what does it grow into inside the ovule? (c) What do the ovule and the ovary become?

Answer: (a) through a pollen tube; (b) a zygote, which becomes an embryo; (c) a seed and a fruit. (a) The pollen grain sends out a tube that grows down the style to the ovary, where the egg cell sits in an ovule (page 121). (b) The fusion of the male and female germ-cells is fertilisation, and it gives the zygote, which divides again and again and becomes an embryo inside the ovule (page 121). (c) The ovule develops a tough coat and becomes a seed; the ovary grows and ripens into a fruit (page 121). Pollen moving from one flower to another, as here, is cross-pollination (page 121).

Eight more: How do Organisms Reproduce? questions with answers.

Chapter 8: Heredity

Q15 (1 mark, multiple choice). A trait that shows up in the plant even when only one of its two gene copies carries it is called (A) recessive (B) dominant (C) acquired (D) halfway

Answer: (B). Sexually reproducing organisms carry two copies of each gene; a trait for which a single copy is enough to show is dominant, and one that shows only when both copies carry it is recessive (pages 130 and 133).

Q16 (3 marks, short answer). In a garden plant, red flowers (R) are dominant over white flowers (r). Two red-flowered plants are crossed, and about one in every four of their seedlings has white flowers. (a) What must the make-up of each parent be? Explain. (b) How does a white-flowered seedling get its colour? (c) What fraction of the seedlings would you expect to have red flowers?

Answer: (a) both Rr; (b) it gets r from each parent; (c) about three quarters. (a) A white seedling must be rr, so each red parent had to pass on an r. A red plant that carries r has one R and one r, so both parents are Rr. (b) Each parent gives one of its two copies to a seedling (page 130); a seedling that gets r from both has no R, and white shows only when both copies are r (page 130). (c) Rr × Rr gives RR, Rr, rR and rr in equal chances, so 3 of every 4 seedlings carry at least one R and are red. This is the same pattern as Mendel's tall and short peas, where one quarter of the F2 plants were short (page 130).

Eight more: Heredity questions with answers. Revision notes: Heredity notes.

Chapter 9: Light – Reflection and Refraction

Q17 (1 mark, multiple choice). In the New Cartesian sign convention, with the object on the left of the mirror, the focal length of a concave mirror is (A) always positive (B) always negative (C) positive for a real image only (D) zero

Answer: (B). Distances are measured from the pole, and those to the left of it (against the incident light) are negative (page 142). The focus of a concave mirror is in front of it, on the left, so f is negative.

Q18 (3 marks, numerical). A dentist holds a small concave mirror of focal length 6 cm near a tooth and wants an upright image twice the size of the tooth. (a) How far from the tooth should the mirror be held? (b) Where is the image, and is it real or virtual? (c) Why does a dentist use a concave mirror and not a convex one?

Answer: (a) 3 cm; (b) 6 cm behind the mirror, virtual; (c) only a concave mirror gives an enlarged upright image. (a) Take f = −6 cm. An upright image twice the size means m = +2, and m = −v/u, so v = −2u (page 143). The mirror formula 1/v + 1/u = 1/f (page 143) gives −1/(2u) + 1/u = 1/(2u) = −1/6, so u = −3 cm: the tooth is 3 cm from the mirror. (b) v = −2 × (−3) = +6 cm. A positive v is behind the mirror, so the image is virtual and upright. Check: 1/6 + 1/(−3) = −1/6. (c) Dentists use concave mirrors because they show the teeth enlarged (page 140); a convex mirror always gives a smaller image.

Eight more: Light questions with answers.

Chapter 10: The Human Eye and the Colourful World

Q19 (1 mark, multiple choice). The part of the eye that controls the size of the pupil is the (A) cornea (B) iris (C) retina (D) ciliary muscle

Answer: (B). The iris, a dark muscular diaphragm behind the cornea, controls the size of the pupil, and the pupil controls how much light enters the eye (page 161).

Q20 (3 marks, short answer). After an evening shower, Kabir sees a rainbow. (a) What in the air acts like small prisms? (b) Describe the three things that happen to sunlight inside one of them. (c) Where is the Sun when he sees the rainbow?

Answer: (a) tiny water droplets; (b) refraction with dispersion, internal reflection, refraction again; (c) behind him. (a) A rainbow is a natural spectrum caused by tiny water droplets in the air dispersing sunlight (page 167). (b) Each droplet refracts and disperses the sunlight entering it, reflects it internally, and refracts it again as it leaves the drop, so different colours reach the eye from different drops (page 167). (c) A rainbow forms in the direction opposite to the Sun, so the Sun is behind the person who sees it (page 167).

Eight more: Human Eye and the Colourful World questions with answers.

Chapter 11: Electricity

Q21 (1 mark, multiple choice). A copper wire has a resistance of 4 Ω. Another copper wire of the same thickness but twice the length has a resistance of (A) 2 Ω (B) 4 Ω (C) 8 Ω (D) 16 Ω

Answer: (C). For the same material and thickness, a wire's resistance grows in step with its length, so twice the length gives 8 Ω (page 178).

Q22 (3 marks, numerical). Two wires are made of the same metal. Wire A is 3 m long with a cross-section of 0.5 mm². Wire B is 1.5 m long with a cross-section of 1.5 mm². (a) Find the ratio of their resistances, R(A) : R(B). (b) Each wire in turn is connected across the same battery. Find the ratio of the currents, I(A) : I(B). (c) Which wire lets current flow more easily?

Answer: (a) 6 : 1; (b) 1 : 6; (c) wire B. (a) R = ρl/A, with the same ρ for both (page 178). R(A) ∝ 3 ÷ 0.5 = 6 and R(B) ∝ 1.5 ÷ 1.5 = 1, so R(A) : R(B) = 6 : 1. (b) By Ohm's law, I = V/R (pages 175-176). With the same V, the current is inversely proportional to the resistance, so I(A) : I(B) = 1 : 6. (c) Wire B, which is shorter and thicker, has one-sixth of A's resistance and carries six times the current.

Eight more: Electricity questions with answers.

Chapter 12: Magnetic Effects of Electric Current

Q23 (1 mark, multiple choice). In Fleming's left-hand rule, with the first finger along the magnetic field and the second finger along the current, the thumb gives the direction of (A) the magnetic field (B) the current (C) the force on the conductor (D) the flow of electrons

Answer: (C). The thumb points in the direction of the motion of, or the force on, the conductor (page 203).

Q24 (3 marks, short answer). In a hostel room, a student plugs an iron, a room heater and a kettle into one socket through a multi-plug, and the fuse blows. (a) What is this situation called? (b) Give two other ways it can happen. (c) How is the fuse connected, and how does it protect the circuit?

Answer: (a) overloading; (b) the live and neutral wires touching, or a sudden rise in the supply voltage; (c) in series, and it stops an unduly high current. (a) Plugging many appliances into one socket can overload the circuit (page 205). (b) Overloading can also happen when the live and neutral wires come into direct contact, for example through damaged insulation, or when the supply voltage rises by accident (page 205). (c) The fuse is connected in series with the appliance (Chapter 11, page 190). When the current becomes too high, the fuse stops it, which protects the wiring and the appliances (page 205).

Eight more: Magnetic Effects of Electric Current questions with answers.

Chapter 13: Our Environment

Q25 (1 mark, multiple choice). In a paddy field, the food chain is rice plants → rats → snakes. The snakes are at the (A) first (B) second (C) third (D) fourth trophic level

Answer: (C). Producers such as rice plants are at the first trophic level, herbivores such as rats at the second, and small carnivores such as snakes at the third (page 210).

Q26 (3 marks, short answer). A housing society starts a compost pit for kitchen waste and a separate bin for plastic. (a) Vegetable peels and tea leaves in the pit turn into compost. What kind of substances are they, and what breaks them down? (b) Why should plastic wrappers not go into the compost pit? (c) Give one change in daily habits that the chapter links to the growing amount of waste.

Answer: (a) biodegradable substances, broken down by biological processes; (b) plastic is non-biodegradable; (c) the shift to disposable things and to non-biodegradable packaging. (a) Substances that biological processes break down are called biodegradable (page 214), and peels and tea leaves rot away in the pit in this way. (b) Substances that are not broken down this way are non-biodegradable: they may be inert and persist for a long time, or may harm members of the ecosystem (page 214), so plastic would stay in the compost. (c) The chapter notes that more and more of what we use has become disposable, and that changes in packaging have made much of our waste non-biodegradable (page 215).

Eight more: Our Environment questions with answers.

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Sources

All opened and read on 3 November 2026. NCERT page numbers are printed page numbers; CBSE page numbers are PDF pages.

The science in each answer is from the textbook pages named. The questions, situations and worked answers are our own, and every number and equation was re-computed by script. This page is general information; follow your teacher, the textbook and CBSE's own notices.

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