CBSE Class 10 Science 2025 Question Paper (Set 31/6/1) with Solutions

1. $\mathrm{2H_2O \rightarrow 2H_2 + O_2}$. Twice as much hydrogen as oxygen forms. Hydrogen collects at the cathode (negative electrode) and oxygen at the anode. Tube P holds the smaller volume, so it is oxygen over the anode R, and Q is hydrogen over the cathode S.
2. So (i) and (iii) are correct.

Answer: (C) (i) and (iii)

1. Potassium nitrate is a salt of a strong acid and a strong base: neutral, pH $7$. Ammonium chloride is a salt of a strong acid and a weak base: acidic, pH below $7$. Sodium carbonate is a salt of a strong base and a weak acid: basic, pH above $7$.
2. So B < A < C.

Answer: (D) B < A < C

1. $\mathrm{2Mg + O_2 \rightarrow 2MgO}$ gives out a lot of heat and light, so it is exothermic, not endothermic. The other three statements are true.

Answer: (C) It is an endothermic reaction.

1. $\mathrm{C_4H_{10}}$, $\mathrm{C_6H_{14}}$ and $\mathrm{C_{10}H_{22}}$ fit the alkane formula $\mathrm{C_nH_{2n+2}}$. $\mathrm{C_7H_{14}}$ fits $\mathrm{C_nH_{2n}}$ (an alkene), a different series.

Answer: (C) $\mathrm{C_7H_{14}}$

1. Iron displaces copper: $\mathrm{Fe + CuSO_4 \rightarrow FeSO_4 + Cu}$. The blue copper sulphate changes to pale green iron(II) sulphate, and reddish-brown copper coats the nail.

Answer: (B) Pale green

Common mistake: Choosing reddish brown. That is the colour of the deposit on the nail, not of the solution.

1. Tamarind contains tartaric acid. (Vinegar has acetic acid, ant sting has methanoic acid and tomato has oxalic acid.)

Answer: (D) Tartaric acid

1. Plaster of Paris is $\mathrm{CaSO_4{\cdot}\tfrac{1}{2}H_2O}$ and washing soda is $\mathrm{Na_2CO_3{\cdot}10H_2O}$. Bleaching powder and baking soda have no water of crystallisation.

Answer: (B) (ii) and (iii)

1. The parents give only $TR$ and $tr$, so every $F_1$ plant is $TtRr$. Tall and round are dominant, so all are tall with round seeds.

Answer: (D) 100% tall with round seeds

1. The hypothalamus, pituitary and pineal glands are in the brain. The thyroid, parathyroid and thymus are in the neck and chest. Only “hypothalamus and pineal” are both in the brain.

Answer: (D) Hypothalamus and Pineal

1. Leishmania divides by binary fission (3). Spirogyra reproduces by fragmentation (4). Planaria regenerates (1). Plasmodium divides by multiple fission (2).

Answer: (C) P-3, Q-4, R-1, S-2

1. The nephron, with its glomerulus and Bowman’s capsule, filters the blood. Each kidney has millions of them.

Answer: (A) Nephron

1. The gastric glands in the stomach wall release hydrochloric acid, the enzyme pepsin and mucus. Bile is made by the liver, trypsin and lipase by the pancreas and amylase by the salivary glands.

Answer: (B) Hydrochloric acid, Pepsin, Mucus

1. A ray parallel to the principal axis is reflected by a concave mirror so that it passes through the principal focus F. Diagram C shows exactly this.

Answer: (C)

1. The pupil is the opening through which light enters, and its size is changed by the iris. CBSE’s key gives the pupil as the part which controls the amount of light entering (the iris is the muscle that changes its size).

Answer: (D) Pupil

About CBSE’s key: Both the iris and the pupil are involved: the iris changes the size of the pupil. CBSE’s key accepts the pupil.

1. Grass is the first level, grasshopper the second and frog the third. Only $10\%$ passes up each level, so the third level has $\dfrac{1}{100}$ of the producers’ energy: $50 \times 100 = 5000$ kJ.

Answer: (D) 5000 kJ

1. Ozone is poisonous, it shields us from UV and it forms from $\mathrm{O_2 + O}$. It is not used as a refrigerant or in fire extinguishers (that is carbon dioxide or CFCs), so statement C is incorrect.

Answer: (C) It is used as a refrigerant and in fire-extinguishers

1. Coal, petrol, LPG and wood are carbon compounds. They are good fuels because they release much heat and light on burning, so R explains A.

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

1. Assertion: true. Reason: false, as xylem runs through the roots, stem and leaves.

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

1. The earth wire goes to a metal plate deep in the ground so that leakage current can flow away, and this keeps the appliance body at earth potential. R explains why A is done.

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

1. Assertion: true. Reason: false. A food web gives many alternative food sources, so it increases the stability of an ecosystem.

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

1. A light green sulphate solution is iron(II) sulphate, so $P$ is iron. The solution turns colourless, so $Q$ displaced iron and formed a colourless sulphate: $Q$ is zinc (or magnesium).
2. $\mathrm{FeSO_4 + Zn \rightarrow ZnSO_4 + Fe}$ (or $\mathrm{FeSO_4 + Mg \rightarrow MgSO_4 + Fe}$).
3. Conclusion: a more reactive metal displaces a less reactive metal from its salt solution, so zinc (or magnesium) is more reactive than iron.

Answer: P = Fe, Q = Zn (or Mg); $\mathrm{FeSO_4 + Zn \rightarrow ZnSO_4 + Fe}$; Zn is more reactive than Fe

1. (a) The brain is protected by the bony box, the skull (cranium), and it is also cushioned by a fluid-filled balloon (the cerebrospinal fluid) around it.
2. (b) The hind-brain, and in it the cerebellum, controls posture and balance.

Answer: (a) the skull and the fluid around it   (b) hind-brain, cerebellum

1. (a) The height of a plant depends on the amount of a plant hormone. How much hormone is made depends on how efficiently an enzyme (a protein) works, and the enzyme is made from a specific DNA sequence (a gene). If the enzyme works efficiently, plenty of hormone is made and the plant is tall.
2. (b) Each cell has two copies of every chromosome, one from each parent. During gamete formation each gamete takes one chromosome from each pair, so it has a single set. When two gametes fuse, the normal number is restored, which keeps the DNA of the species stable.

Answer: (a) gene → enzyme → hormone → tallness   (b) gametes have one set; fertilisation restores two

1. (a) The ray bends away from the normal in Medium 2, so Medium 2 is the rarer medium and the speed of light is more in Medium 2.
2. (b) Light bends away from the normal when it goes from an optically denser medium to an optically rarer one, because its speed increases.
3. (c) $n_{21} = \dfrac{\text{speed of light in medium 1}}{\text{speed of light in medium 2}}$.

Answer: (a) Medium 2   (b) denser to rarer   (c) $n_{21} = \dfrac{v_1}{v_2}$

1. (a)(i) At very high altitude there is hardly any air or dust to scatter the sunlight, so scattering is not prominent and the sky looks dark. (ii) Red light is scattered the least by smoke or fog because it has the longest wavelength, so it can be seen from far away.
2. (b) A rainbow is a natural spectrum appearing in the sky after a rain shower. After the rain, small water droplets are present in the air and act like tiny prisms: light is refracted and dispersed in them, and then reflected and refracted again.

Answer: (a) little scattering; red scatters least   (b) a spectrum made by water droplets, present only after rain

1. Natural ponds and lakes have natural cleansing agents such as microbes (decomposers) which clean them. An aquarium or a swimming pool is an artificial ecosystem and has no decomposers.
2. If it is not cleaned regularly, the waste keeps increasing, which is harmful to the fishes and the aquatic plants.

Answer: Natural ponds have decomposers; an aquarium does not, so its waste builds up

1. (a) $\mathrm{3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2}$.
2. (b) $\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$.
3. (c) $\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy}$.

Answer: (a) $3\mathrm{Fe} + 4\mathrm{H_2O} \rightarrow \mathrm{Fe_3O_4} + 4\mathrm{H_2}$   (b) $\mathrm{CH_4} + 2\mathrm{O_2} \rightarrow \mathrm{CO_2} + 2\mathrm{H_2O}$   (c) $\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O}$

1. (a)(i) Baking soda is a mild, non-corrosive basic salt, so it neutralises the excess acid in the stomach. (ii) It gives off carbon dioxide on reacting with a mild edible acid (tartaric acid), which makes the cake rise. (iii) In a fire extinguisher it acts as a base, reacts with the acid and gives carbon dioxide that puts out the fire.
2. (b)(i) $\mathrm{Zn + 2HCl \rightarrow ZnCl_2 + H_2}$ (zinc chloride and hydrogen). (ii) $\mathrm{2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O}$ (sodium sulphate). (iii) $\mathrm{Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2}$ (sodium chloride).

Answer: (a) basic (neutralises acid); releases CO₂ with an acid   (b) salt + hydrogen; salt + water; salt + water + CO₂

1. (i) The pulmonary vein brings oxygenated blood from the lungs. (ii) The vena cava brings deoxygenated blood from the body.
2. The right atrium receives the deoxygenated blood. It contracts and the blood passes into the right ventricle, which contracts and pumps the blood into the lungs through the pulmonary artery.

Answer: (i) pulmonary vein   (ii) vena cava; right atrium → right ventricle → pulmonary artery to the lungs

1. (a) All the $F_1$ plants had purple flowers. No white-flowered plants were seen and no plants had mixed colours, so only the dominant trait of the parents showed. (All are $Ww$.)
2. (b) Selfing $Ww \times Ww$ gives $WW : Ww : ww = 1 : 2 : 1$. (i) White flowers need $ww$: $25\%$. (ii) $1 : 2 : 1$.
3. (c) A dominant trait expresses itself even when the contrasting trait is present, while a recessive trait stays hidden (unexpressed) in the presence of its contrasting trait.

Answer: (a) all purple; no white or mixed   (b) 25%; 1 : 2 : 1   (c) dominant shows in the presence of the other trait; recessive does not

1. (a) In observation 4 the object and image distances are equal ($-30$ cm and $+30$ cm). This happens only when the object is at $2f$, so $2f = 30$ cm and $f = +15$ cm.
2. (b) Observation 8 is not correct. The flame is at $12$ cm, which is less than $f = 15$ cm, so the object lies between the lens and the focus. Then the image is virtual and on the same side as the object, so it cannot be focused on a screen and $v$ cannot be $+120$ cm. (CBSE says $v$ should be $-120$ cm; by the lens formula it would actually be $-60$ cm, but the row is wrong either way.)
3. (c) Take a correct set, for example observation 3 (u = −40 cm, v = +24 cm): the object is between $2F$ and $F$... more exactly beyond $2F$ (30 cm), so the image is real, inverted and smaller, between $F$ and $2F$ on the other side (diagram above).

Answer: (a) $f = +15$ cm (object at $2f$ gives image at $2f$)   (b) observation 8 (object inside $f$)   (c) ray diagram

About CBSE’s key: The key says the image distance in observation 8 should be −120 cm. The lens formula gives −60 cm. The point of the question (observation 8 is the wrong one) is unaffected.

1. (a) A positive power means a convex lens, which corrects hypermetropia (far-sightedness).
2. (b) The eyeball has become too small (shortened), or the focal length of the eye lens is too long (the lens is less convergent).
3. (c) $f = \dfrac{1}{P} = \dfrac{1}{+2.0} = +0.5$ m $= +50$ cm.

Answer: (a) hypermetropia   (b) small eyeball; long focal length of the eye lens   (c) $+0.5$ m

1. (a) The potential difference between two points is 1 volt if 1 joule of work is done to move a charge of 1 coulomb from one point to the other.
2. (b)(i) An ammeter: it measures the electric current in a circuit. (ii) A rheostat (variable resistance): it is used to vary the resistance, and so the current, in a circuit.

Answer: (a) 1 J of work per 1 C   (b) ammeter measures current; rheostat varies the resistance

1. (a) The alcohol is ethanol, $\mathrm{CH_3CH_2OH}$ ($\mathrm{H{-}C(H)(H){-}C(H)(H){-}O{-}H}$), and the acid is ethanoic acid, $\mathrm{CH_3COOH}$ ($\mathrm{H{-}C(H)(H){-}C(=O){-}O{-}H}$).
2. Oxidising ethanol with alkaline potassium permanganate or acidified potassium dichromate, with heating, gives the acid: $\mathrm{C_2H_5OH \xrightarrow{alk.\ KMnO_4,\ heat} CH_3COOH}$.
3. In the presence of an acid catalyst they react to form an ester (esterification): $\mathrm{C_2H_5OH + CH_3COOH \xrightarrow{acid} CH_3COOC_2H_5 + H_2O}$, ethyl ethanoate, a sweet-smelling ester.
4. (b) Soaps are sodium or potassium salts of long-chain carboxylic acids. A soap molecule has a long hydrocarbon tail, which is hydrophobic (water-repelling), and an ionic head, which is hydrophilic (water-loving).
5. Most dirt is oily and does not dissolve in water. In water the soap molecules form micelles: the tails point inwards and trap the oily dirt, and the heads point outwards towards the water. The micelles form an emulsion, which pulls the dirt out of the cloth and rinses off in water.
6. Hard water contains calcium and magnesium salts, which react with soap to form an insoluble scum, so little foam forms and the soap is wasted. The problem is overcome by using detergents, or by removing the hardness of the water.

Answer: (a) ethanol and ethanoic acid; oxidation with $\mathrm{KMnO_4}$; esterification gives ethyl ethanoate   (b) soaps are salts of fatty acids; micelles; scum in hard water; use detergents

1. (a) Puberty is the period of adolescence when the general body growth slows down and the reproductive tissues begin to mature. In boys: the voice cracks, thick hair grows on the face, and hair grows in the armpits and genital area.
2. (b) Sperm formation needs a temperature lower than the normal body temperature, so the testes lie in the scrotum, outside the abdominal cavity.
3. (c) Techniques of contraception: a mechanical barrier (a condom); chemical methods (oral pills); the loop or copper-T placed in the uterus; surgical methods (blocking the vas deferens or the fallopian tube). Oral pills and the copper-T are not meant for males.
4. (OR)(a) (i) Ovary. (ii) Oviduct (fallopian tube). (iii) Uterus. (iv) Vagina.
5. (b)(i) After the zygote is implanted it starts dividing. The uterine lining thickens and is richly supplied with blood vessels to nourish the developing embryo, and the placenta develops to give oxygen and food to it and take away waste. (ii) If the egg is not fertilised, the uterine lining slowly breaks down and comes out as blood and mucus along with the unfertilised egg.

Answer: (a) slowing of growth and maturing of reproductive tissue; voice change, facial hair   (b) cooler temperature   (c) condom, pills, loop, surgery; pills and loop not for males (OR) ovary, oviduct, uterus, vagina; thick lining and placenta; menstruation

1. (a) Magnetic field lines are imaginary lines around a magnet that show the magnetic field. The direction of the field at a point is found by placing a small compass needle there: the direction its north pole points is the direction of the field.
2. For a circular loop, the field lines are concentric circles near the wire, which become larger and straighter farther away, and at the centre of the loop the line is straight, perpendicular to the plane of the loop (diagram above, with the current and field directions marked).
3. The magnitude of the field depends on the amount of current through the coil, on the number of turns in the coil and on the radius of the coil. (Any two.)
4. (b) If two lines crossed, at the point of intersection a compass needle would point in two directions at the same point, which is not possible.
5. The pattern for a solenoid is shown in the second diagram. Inside the solenoid the lines are parallel and equally spaced, so the magnetic field is the same (uniform) at all points inside it. The field of a solenoid depends on the number of turns, the current in it and the core material inside it. (Any two.)

Answer: (a) lines show the field; a compass needle gives its direction; current and number of turns (b) lines would have two directions at one point; uniform field inside a solenoid

1. (I) The electrical conductivity decreases, and the melting point is usually lower than that of the pure metal (in a few cases it can be higher).
2. (II) Solder, an alloy of lead (Pb) and tin (Sn).
3. (III)(a) An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. Brass is prepared by mixing copper and zinc in a definite proportion.
4. (b) Stainless steel is an alloy of steel (iron) with nickel and chromium. Iron is first mixed with a little carbon (about 0.05%) so that it becomes hard and strong, and then nickel and chromium are mixed in. It does not rust, which is why it is good for utensils.

Answer: (I) conductivity falls, melting point falls   (II) solder: lead and tin   (III) alloy = mixture; brass = Cu + Zn (OR) steel + Ni + Cr; does not rust

1. (I) Geotropism: X (the root) shows positive geotropism and Y (the shoot) shows negative geotropism (and the shoot shows positive phototropism).
2. (II) (i) Abscisic acid. (ii) Cytokinin.
3. (III)(a) The plant uses electrical-chemical means to pass the information about the touch from cell to cell. The cells then change shape by changing the amount of water in them: some swell and some shrink, so the leaves move.
4. (b) Auxin. When light comes from one side, auxin diffuses towards the shady side of the shoot. There it makes the cells grow longer, so the side away from the light grows more and the plant bends towards the light.

Answer: (I) geotropism   (II) abscisic acid; cytokinin   (III) electrical-chemical signals, cells change shape with water (OR) auxin on the shady side

1. (I) Join X and Y side by side (in parallel) across the battery, keep the ammeter in the main line and connect the voltmeter across the parallel pair (diagram above).
2. (II) (i) In the parallel combination, the potential difference is the same across X and Y. (ii) In the series combination, the same current flows through X and Y.
3. (III)(a) In series $R = 3 + 6 = 9\ \Omega$. $I = \dfrac{V}{R} = \dfrac{2}{9} = 0.22$ A.
4. (b) In parallel: $\dfrac{1}{R} = \dfrac{1}{3} + \dfrac{1}{6} = \dfrac{3}{6} = \dfrac{1}{2}$, so $R = 2\ \Omega$.

Answer: (II) (i) parallel (ii) series   (III) $I = 0.22$ A (OR) $R = 2\ \Omega$