CBSE Class 10 Science 2025 Question Paper (Set 31/4/1) with Solutions

1. Milk turning sour, fermentation of grapes and rusting of iron all form new substances: chemical reactions.
2. Melting of a glacier only changes ice to water, a physical change in state with no new substance.

Answer: (D) Melting of glaciers

1. The drying agent must absorb moisture but not react with HCl. Calcium oxide, hydroxide and carbonate are basic, so they would react with the acid gas.
2. Calcium chloride is neutral and takes up water, so it is used.

Answer: (A) Calcium chloride

1. Drawing into wires is ductility. (Beating into thin sheets is malleability.)

Answer: (B) ductility

1. Propyne is $\mathrm{CH_3{-}C{\equiv}CH}$: the three carbons have one C–C single bond and one C≡C triple bond. Butyne has two single bonds as well, and benzene and cyclohexane have rings.

Answer: (D) Propyne

1. Proteins are made of amino acids, which contain nitrogen. Plants take it from the soil as nitrates and nitrites.

Answer: (B) Nitrogen

1. Lymph drains back into larger veins, not arteries, so D is true and A is false.
2. Lymph is like blood plasma and carries proteins and white blood cells but no red blood cells. B (“blood cells”, i.e. the white ones) is the accepted true statement and C is false.

Answer: (B) B and D

1. Rose and banana are propagated by vegetative methods (cutting, grafting, suckers). Over time they have lost the capacity to produce viable seeds.

Answer: (C) seeds

1. The anther makes the pollen grains, which carry the male gametes. The ovary and stigma are female parts, and the filament only holds up the anther.

Answer: (A) anther

1. $TT \times tt$ gives all $Tt$ in $F_1$, and tall is dominant: $100\%$ tall.
2. Selfing $Tt \times Tt$ gives $TT : Tt : tt = 1 : 2 : 1$, so $75\%$ are tall in $F_2$.

Answer: (C) 100%; 75%

1. $m = -1$ means a real, inverted image of the same size as the object. That happens when the object is at $2f$: $u = -2 \times 20 = -40$ cm. Check: $\dfrac{1}{v} = \dfrac{1}{f} + \dfrac{1}{u} = \dfrac{1}{20} - \dfrac{1}{40} = \dfrac{1}{40}$, so $v = 40$ cm and $m = \dfrac{v}{u} = -1$ ✓.

Answer: (C) 40 cm

1. A rectangular glass slab bends the ray towards the normal on entering and away from the normal on leaving by equal amounts. The emergent ray is parallel to the incident ray, but shifted sideways (lateral displacement).

Answer: (C) glass slab

1. The key takes this as cutting the wire into three equal pieces along its length. Each piece has length $\dfrac{l}{3}$, so its resistance is $\dfrac{R}{3}$.
2. In parallel: $\dfrac{1}{R'} = \dfrac{3}{R} + \dfrac{3}{R} + \dfrac{3}{R} = \dfrac{9}{R}$, so $R' = \dfrac{R}{9}$ and $\dfrac{R}{R'} = 9$.

Answer: (D) 9

About CBSE’s key: The word “lengthwise” could also mean cutting along the wire (into three thinner wires), which would give R′ = R. CBSE’s key follows the reading of three equal pieces cut across the length, so the answer is 9.

1. $R = \dfrac{V^2}{P} = \dfrac{220 \times 220}{11} = 4400\ \Omega$.

Answer: (A) $4400\ \Omega$

1. Each bulb must have $4$ V across it. In series the voltage divides equally, so the number of bulbs is $\dfrac{240}{4} = 60$. (Each carries $\dfrac{6}{4} = 1.5$ A, the same current as its rating.)

Answer: (C) 60

1. Only about $10\%$ of the energy passes to the next level, so the fewer the steps, the more energy reaches the last consumer.
2. Plants → Man has the fewest trophic levels (two), so it is the most efficient.

Answer: (C) Plants → Man

1. DDT, a pesticide, is not broken down, so it is passed up the food chain and builds up at each higher trophic level. CO and CFCs are gases, and manure is biodegradable.

Answer: (C) DDT

1. In large animals diffusion alone is too slow, so oxygen does not reach all parts easily. That is why they need respiratory pigments such as haemoglobin to carry oxygen. So A is false and R is true.

Answer: (D) A is false, but R is true

1. The correct way is to add the acid slowly to water with stirring, because dissolving gives out much heat. So A is false. R is true.

Answer: (D) A is false, but R is true

Common mistake: Adding water to the acid. Always add acid to water.

1. In some reptiles the incubation temperature decides the sex, which means that sex is not decided by chromosomes in them. So R explains A.

Answer: (A) Both A and R are true and R is the correct explanation of A

1. When the ciliary muscles contract, the lens becomes thicker (its focal length gets shorter, for seeing near objects). They relax to make it thin. So A is false. R is true.

Answer: (D) A is false, but R is true

1. Oxidation is the gain of oxygen by a substance (or the loss of hydrogen, or the loss of electrons).
2. In $\mathrm{CuO + H_2 \rightarrow Cu + H_2O}$, hydrogen gains oxygen to form water, so hydrogen ($\mathrm{H_2}$) is oxidised. (Copper oxide loses oxygen: it is reduced.)

Answer: Hydrogen is oxidised

1. (A) Magnesium (2, 8, 2) gives its two outer electrons, one to each of two chlorine atoms (2, 8, 7), which each need one. So $\mathrm{Mg \rightarrow Mg^{2+} + 2e^-}$ and $\mathrm{Cl + e^- \rightarrow Cl^-}$ for each chlorine. The compound is $\mathrm{MgCl_2}$. Cation: magnesium ion, $\mathrm{Mg^{2+}}$. Anion: chloride ion, $\mathrm{Cl^-}$.
2. (B) If the ore is zinc sulphide: roasting, $\mathrm{2ZnS + 3O_2 \xrightarrow{heat} 2ZnO + 2SO_2}$, then reduction with carbon, $\mathrm{ZnO + C \xrightarrow{heat} Zn + CO}$.
3. If the ore is zinc carbonate: calcination, $\mathrm{ZnCO_3 \xrightarrow{heat} ZnO + CO_2}$, then reduction, $\mathrm{ZnO + C \xrightarrow{heat} Zn + CO}$.

Answer: (A) $\mathrm{Mg^{2+}}$ and $\mathrm{Cl^-}$   (B) roasting or calcination, then reduction with carbon

1. Plants use these ways to get rid of wastes:
2. 1. Oxygen, a waste of photosynthesis, leaves through the stomata. 2. Excess water goes out by transpiration. 3. Waste is stored in leaves, which are then shed. 4. Wastes are stored as resins and gums in old xylem. (Also: waste is stored in cell vacuoles, or given out into the soil.)

Answer: Oxygen through stomata; transpiration; shedding of leaves; resins and gums in old xylem

1. A woman has two X chromosomes (XX), so all her eggs carry an X. A man has one X and one Y (XY), so half his sperms carry X and half carry Y.
2. If an X sperm fertilises the egg, the child is XX: a girl. If a Y sperm fertilises it, the child is XY: a boy. So the sperm, that is the father, decides the sex of the child.

Answer: X sperm + X egg gives a girl; Y sperm + X egg gives a boy

1. (A) The ray bends towards the normal on entering the prism and away from the normal on leaving, so it is deviated towards the base. The angle δ between the original direction and the emergent ray is the angle of deviation (diagram above).
2. (B) Presbyopia is corrected with bifocal lenses. The upper part is a concave lens, for seeing distant objects, and the lower part is a convex lens, for reading and seeing near objects. (A convex lens alone also corrects the near vision.) The two parts are designed so that the person can see both far and near clearly.

Answer: (A) angle of deviation δ   (B) bifocal lens: concave upper part, convex lower part

1. Magnetic field lines are the lines that represent the magnetic field around a magnet: the path along which a free north pole would tend to move.
2. Properties (any two): no two field lines cross each other; outside the magnet they go from the north pole to the south pole; they are closed curves; inside the magnet they go from south to north; they are closer where the field is stronger.

Answer: Lines showing the field; they never cross and are closed curves

1. (A) We balance an equation so that the number of atoms of each element is the same before and after the reaction. This follows the law of conservation of mass: mass can neither be created nor destroyed in a chemical reaction.
2. $\mathrm{3Zn + 2H_3PO_4 \rightarrow Zn_3(PO_4)_2 + 3H_2}$.
3. (B) A reaction in which an insoluble solid (a precipitate) is formed is a precipitation reaction. Example: sodium sulphate solution added to barium chloride solution gives a white precipitate of barium sulphate.
4. $\mathrm{Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)}$.

Answer: (A) $3\mathrm{Zn} + 2\mathrm{H_3PO_4} \rightarrow \mathrm{Zn_3(PO_4)_2} + 3\mathrm{H_2}$; law of conservation of mass   (B) $\mathrm{BaSO_4}$ precipitate

1. Take an aluminium or copper wire and clamp it to a stand. Fix a pin to the free end of the wire with a little wax.
2. Heat the wire with a spirit lamp or a burner near the clamped end.
3. Observation: the heat travels along the wire, the wax melts and the pin falls, but the wire itself does not melt.
4. Conclusion: metals are good conductors of heat (the heat reached the far end quickly) and have a high melting point (the wire did not melt in the flame).

Answer: The wax melts and the pin falls, but the wire does not melt

1. (i) Saliva contains salivary amylase, which breaks down starch into sugar (maltose).
2. (ii) Bile juice contains bile salts. They make the food coming from the stomach alkaline and emulsify fats (break large globules into smaller ones).
3. (iii) Pancreatic juice contains trypsin, which digests proteins, and lipase, which breaks down the emulsified fats.

Answer: (i) amylase: starch to sugar   (ii) bile salts: make food alkaline, emulsify fats   (iii) trypsin and lipase

1. Limitations: (1) electrical impulses reach only the cells that are connected by nervous tissue, not every cell in the body; (2) once a cell has generated and sent an impulse, it takes some time to reset before it can send another.
2. Chemical communication is better because the chemical signals (hormones) can reach all the cells of the body, steadily and for a long time, so they bring about the desired changes everywhere, not just in connected cells.

Answer: Impulses reach only connected cells and need time to reset; chemical signals reach all cells

1. A concave mirror gives a virtual, erect, magnified image only when the object is between the pole $P$ and the focus $F$, that is less than $18$ cm from the mirror.
2. To check: $f = -18$ cm and $m = +2 = -\dfrac{v}{u}$, so $v = -2u$.
3. Mirror formula $\dfrac{1}{v} + \dfrac{1}{u} = \dfrac{1}{f}$: $-\dfrac{1}{2u} + \dfrac{1}{u} = \dfrac{1}{2u} = -\dfrac{1}{18}$, so $u = -9$ cm.
4. The object is $9$ cm in front of the mirror, between $P$ and $F$, and the image is $18$ cm behind the mirror: virtual, erect and twice as large.

Answer: Between $P$ and $F$; $u = -9$ cm

1. (i) A has an extremely high resistivity: an insulator. C has a very low resistivity: a conductor. B lies in between and is far higher than the metals: an alloy.
2. (ii) A: plastic (or rubber), used for the handle of an electric iron. B: nichrome, used as the heating element of an electric iron or stove. C: copper, used for the connecting wires.

Answer: (i) A insulator, B alloy, C conductor   (ii) plastic handle, nichrome heating element, copper wires

1. Decomposers are micro-organisms that break down complex organic substances (dead plants and animals) into simple inorganic substances.
2. Examples: bacteria and fungi.
3. The simple substances go into the soil and are taken up again by the plants. So the nutrients are recycled and the balance of the ecosystem is maintained.

Answer: They break down dead matter into simple substances that plants use again; bacteria and fungi

1. (A) Burning $C$ gives $2$ mol $\mathrm{CO_2}$ and $3$ mol $\mathrm{H_2O}$: $\mathrm{C_2H_6 + \tfrac{7}{2}O_2 \rightarrow 2CO_2 + 3H_2O}$, so $C$ is ethane, $\mathrm{CH_3{-}CH_3}$. Adding one mole of $\mathrm{H_2}$ with nickel means $B$ is ethene, $\mathrm{CH_2{=}CH_2}$. Dehydration with conc. $\mathrm{H_2SO_4}$ gives ethene, so $A$ is ethanol, $\mathrm{CH_3CH_2OH}$.
2. $\mathrm{CH_3CH_2OH \xrightarrow{conc.\ H_2SO_4,\ heat} CH_2{=}CH_2 + H_2O}$ and $\mathrm{CH_2{=}CH_2 + H_2 \xrightarrow{Ni} CH_3CH_3}$.
3. Role of conc. sulphuric acid: it is a dehydrating agent, it removes water from ethanol.
4. (B)(i) $A$ is ethanoic acid (acetic acid), $\mathrm{CH_3COOH}$: the carbon with a $\mathrm{C{=}O}$ and an $\mathrm{{-}OH}$ attached to a $\mathrm{CH_3}$ group.
5. (ii) $\mathrm{CH_3COOH + C_2H_5OH \xrightarrow{acid} CH_3COOC_2H_5 + H_2O}$ (ethyl ethanoate, $B$, an ester). The acid acts as a catalyst.
6. (iii) By adding sodium hydroxide solution to the ester (saponification gives the sodium salt of the acid), and then acidifying; or by hydrolysis of the ester with an acid or base.
7. (iv) By oxidising ethanol with alkaline potassium permanganate or acidified potassium dichromate, on warming.
8. (v) Carbon dioxide, $\mathrm{CO_2}$.

Answer: (A) A ethanol, B ethene, C ethane; $\mathrm{H_2SO_4}$ is a dehydrating agent   (B) ethanoic acid; ester; hydrolysis; oxidation; $\mathrm{CO_2}$

1. (A)(i) Regeneration is the ability of an organism to give rise to a new individual from its body parts: if it is cut into pieces, each piece can grow into a new organism. Planaria or Hydra shows it. Spirogyra does not (some complex animals do not either), because it does not have specialised cells which multiply to make the new cell types and tissues.
2. (ii) The filamentous green structures are Spirogyra (algae). They reproduce by fragmentation: on maturing the filament breaks up into smaller pieces, and each piece grows into a new individual.
3. (B)(i) (a) Vas deferens. (b) Testes. (c) Prostate gland (and seminal vesicles). (d) Scrotum.
4. (ii) A sperm contains the genetic material (in its head), has a tail for movement, and is small in size.
5. (iii) Surgical methods block the path of the gametes: in males the vas deferens is blocked (vasectomy) and in females the fallopian tube is blocked (tubectomy), so fertilisation cannot take place. Side effect: infection if the surgery is not done properly.

Answer: (A) planaria regenerates, Spirogyra does not; fragmentation   (B) vas deferens, testes, prostate, scrotum; vasectomy and tubectomy

1. (A)(i) Each wire has concentric circular field lines around it: clockwise around the wire with current into the page and anticlockwise around the wire with current out of the page (diagram above, with the current in the left conductor taken as into the page). At the point O between the two wires, both fields point in the same direction, along the line joining down the page, so they add up.
2. (ii)(a) The red wire is the live wire, the black wire is the neutral wire and the green wire is the earth wire. (b) The potential difference between the live (red) and the neutral (black) wire is $220$ V.
3. (c) The earth wire is a safety measure. If current leaks to the metallic body of the appliance, the earth wire gives it a low-resistance path to the ground and keeps the body at the potential of the earth, so the user does not get a severe electric shock.
4. (B)(i)(a) On closing the key, current flows through the rod AB placed in the field of the horseshoe magnet and the rod is displaced (it moves), which shows a force acts on it. (b) The direction of the force can be reversed by reversing the direction of the current, or by reversing the direction of the magnetic field (by interchanging the poles).
5. (ii) The force is the greatest when the current is at right angles to the direction of the magnetic field.
6. (iii) Fleming’s left-hand rule: stretch the thumb, the forefinger and the middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force on the conductor.

Answer: (A) opposite currents: fields add at O; live (red), neutral (black), earth (green); 220 V; low-resistance path to earth   (B) AB moves; reverse current or field; highest when I ⟂ B; Fleming’s rule

1. (i) Hydrochloric acid (HCl) and sodium hydroxide (NaOH).
2. (ii) Neutral, because it is a salt of a strong acid (HCl) and a strong base (NaOH).
3. (iii)(A) The brine is electrolysed (the chlor-alkali process). Sodium hydroxide solution forms near the cathode, chlorine gas at the anode and hydrogen gas at the cathode.
4. (iii)(B) $\mathrm{NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3}$. Heating the baking soda gives sodium carbonate: $\mathrm{2NaHCO_3 \xrightarrow{heat} Na_2CO_3 + H_2O + CO_2}$. Recrystallising sodium carbonate gives washing soda: $\mathrm{Na_2CO_3 + 10H_2O \rightarrow Na_2CO_3{\cdot}10H_2O}$.

Answer: (i) HCl and NaOH   (ii) neutral   (iii) NaOH and H₂ at the cathode, Cl₂ at the anode (OR) washing soda from baking soda

1. (i) A reflex action: a sudden, automatic response to a stimulus in the environment, without thinking.
2. (ii)(a) The motor neuron carries the message from the spinal cord to the effector organ (the muscle). (b) The relay neuron connects the sensory neuron to the motor neuron.
3. (iii)(A) The central nervous system, made of the brain and the spinal cord, and the peripheral nervous system, made of the cranial nerves and the spinal nerves.
4. (B) (a) Thinking: the fore-brain (cerebrum). (b) Picking up a pencil: the cerebellum (hind-brain), which coordinates precise movements. (c) Blood pressure: the medulla (hind-brain). (d) Hunger: the fore-brain.

Answer: (i) reflex action   (ii) motor neuron to muscle; relay neuron joins sensory to motor   (iii) CNS and PNS (OR) cerebrum, cerebellum, medulla, fore-brain

1. (i) A rainbow (also, for example, the colours seen in a soap bubble).
2. (ii) The white light is dispersed (split) into its seven colours by the prism, because each colour bends by a different angle.
3. (iii)(A) Two conditions: water droplets must be present in the atmosphere, and the Sun must be at the back of the observer.
4. (iii)(B) Dispersion happens at the first refraction as the light enters the droplet (a), the colours are reflected internally at the back of the droplet (b), and the final refraction happens as the light leaves the droplet (c) (diagram above).

Answer: (i) rainbow   (ii) dispersion   (iii) water droplets and the Sun behind the observer (OR) diagram with a, b, c