CBSE Class 10 · Science · board exam 2027
CBSE Class 10 Science Question Paper 2025
The board’s 2025 question paper, set 31/1/1 — all 39 questions as printed; 20 objective answers from the board’s own key; full model answers for 3 written questions, how the answer begins for 7 more. Each question names its chapter, where that chapter’s most-asked questions are.
Full marks 80 · Time 3 h
Section A · Objective questions (20)
Electrolysis of water is a decomposition reaction. The mass ratio (MH : MO) of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is :
- (A) 8 : 1
- (B) 2 : 1
- (C) 1 : 2
- (D) 1 : 8 ✓
Answer (the board’s key): (D)
The products formed when Aluminium and Magnesium are burnt in the presence of air respectively are :
- (A) Al3O4 and MgO2
- (B) Al2O3 and MgO ✓
- (C) Al3O4 and MgO
- (D) Al2O3 and MgO2
Answer (the board’s key): (B)
The following table shows the pH values of four solutions A, B, C and D on a pH scale : [figure: pH scale with values marked] The solutions A, B, C and D respectively are of a
- (A) Strong acid, weak acid, neutral, strong base
- (B) Weak acid, neutral, weak base, strong base
- (C) Weak acid, neutral, strong base, weak base
- (D) Weak acid, neutral, strong base, strong acid ✓
Answer (the board’s key): (D)
Consider the following reactions : (i) Dilute hydrochloric acid reacts with sodium hydroxide. (ii) Magnesium oxide reacts with dilute hydrochloric acid. (iii) Carbon dioxide reacts with sodium hydroxide. It is observed that in each case :
- (A) Salt and water are formed. ✓
- (B) Neutral salts are formed.
- (C) Hydrogen gas is formed.
- (D) Acidic salts are formed.
Answer (the board’s key): (A)
Reaction between two elements A and B, forms a compound C. A loses electrons and B gains electrons. Which one of the following properties will not be shown by compound C ?
- (A) It has high melting point.
- (B) It is highly soluble in water.
- (C) It has weak electrostatic forces of attraction between its oppositely charged ions. ✓
- (D) It conducts electricity in its molten state or aqueous solution.
Answer (the board’s key): (C)
The metals obtained from their molten chlorides by the process of electrolytic reduction are :
- (A) Gold and silver
- (B) Calcium and magnesium ✓
- (C) Aluminium and silver
- (D) Sodium and iron
Answer (the board’s key): (B)
The formation of magnesium oxide is correctly shown in option :
- (A) Mg : [O][electron dot diagram] -> Mg2+ [O]2- ✓
- (B) Mg . -> [O] -> Mg+ [O]-
- (C) Mg : + [O][O] -> Mg2+ [O-]2
- (D) 2Mg x -> O: -> [Mg2+]2 [O]2-
Answer (the board’s key): (A)
Secretion of less saliva in mouth will effect the conversion of :
- (A) proteins into amino acids
- (B) fats into fatty acids and glycerol
- (C) starch into simple sugars ✓
- (D) sugars into alcohol
Answer (the board’s key): (C)
The plant hormone whose concentration stimulates the cells to grow longer on the side of the shoot which is away from light is :
- (A) Cytokinins
- (B) Gibberellins
- (C) Adrenaline
- (D) Auxins ✓
Answer (the board’s key): (D)
The correct/true statement(s) for a bisexual flower is/are : (i) They possess both stamen and pistil. (ii) They possess either stamen or pistil. (iii) They exhibit either self-pollination or cross-pollination. (iv) They cannot produce fruits on their own.
- (A) (i) only
- (B) (iv) only
- (C) (i) and (iii) ✓
- (D) (i) and (iv)
Answer (the board’s key): (C)
If pea plants with round and green seeds (RRyy) are crossed with pea plants having wrinkled and yellow seeds (rrYY), the seeds developed by the plants of F1 generation will be :
- (A) 50% round and green
- (B) 75% wrinkled and green
- (C) 100% round and yellow ✓
- (D) 75% wrinkled and yellow
Answer (the board’s key): (C)
The breakdown of glucose has taken the following pathway : Glucose --(a)--> Pyruvate + Energy --(b)--> Lactic acid + Energy The sites 'a' and 'b' respectively are :
- (A) Mitochondria and Oxygen deficient muscle cells
- (B) Cytoplasm and Oxygen rich muscle cells
- (C) Cytoplasm and Yeast cells
- (D) Cytoplasm and Oxygen deficient muscle cells ✓
Answer (the board’s key): (D)
Mirror 'X' is used to concentrate sunlight in solar furnace and Mirror 'Y' is fitted on the side of the vehicle to see the traffic behind the driver. Which of the following statements are true for the two mirrors ? (i) The image formed by mirror 'X' is real, diminished and at its focus. (ii) The image formed by mirror 'Y' is virtual, diminished and erect. (iii) The image formed by mirror 'X' is virtual, diminished and erect. (iv) The image formed by mirror 'Y' is real, diminished and at its focus.
- (A) (i) and (ii) ✓
- (B) (ii) and (iii)
- (C) (iii) and (iv)
- (D) (i) and (iv)
Answer (the board’s key): (A)
An old person is suffering from an eye defect caused by weakening of ciliary muscles and diminishing flexibility of the eye lens. If the defect of vision is ‘a’ which can be corrected by lens ‘b’, then ‘a’ and ‘b’ respectively are :
- (A) hypermetropia and convex lens
- (B) presbyopia and bifocal lens ✓
- (C) myopia and concave lens
- (D) myopia and bifocal lens
Answer (the board’s key): (B)
Which of the following groups do not constitute a food chain ? (i) Wolf, rabbit, grass, lion (ii) Plankton, man, grasshopper, fish (iii) Hawk, grass, snake, grasshopper, frog (iv) Grass, snake, wolf, tiger
- (A) (i) and (iv)
- (B) (i) and (iii)
- (C) (ii) and (iii)
- (D) (ii) and (iv) ✓
Answer (the board’s key): (D)
The percentage of solar energy which is not converted into food energy by the leaves of green plants in a terrestrial ecosystem is about :
- (A) 1%
- (B) 10%
- (C) 90%
- (D) 99% ✓
Answer (the board’s key): (D)
Assertion (A) : Decomposition reactions are generally endothermic reactions. Reason (R) : Decomposition of organic matter into compost is an exothermic process.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). ✓
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer (the board’s key): (B)
Assertion (A) : A human child bears all the basic features of human beings. Reason (R) : It looks exactly like its parents, showing very little variations.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false. ✓
- (D) Assertion (A) is false, but Reason (R) is true.
Answer (the board’s key): (C)
Assertion (A) : No two magnetic field lines are found to cross each other. Reason (R) : The compass needle cannot point towards two directions at the point of intersection of two magnetic field lines.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). ✓
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer (the board’s key): (A)
Assertion (A) : The amount of ozone in the atmosphere began to drop sharply in the 1980s. Reason (R) : The oxygen atoms combine with molecular oxygen to form ozone.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). ✓
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Answer (the board’s key): (B)
Section B · Written questions (19)
A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place.
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Model answer · observations of a chemical change
- 1.Gas bubbles are given off (a gas is evolved), which shows that a new substance has formed.1 mark
- 2.A precipitate forms or the colour changes, which also shows that a new substance has formed — so a chemical change has taken place.1 mark
Marks split from a structure derived from past papers (checked twice); not CBSE’s official scheme
Draw labelled diagrams to show different stages of budding in Hydra.
(a) Besides minimising the loss of blood, why is it essential to plug any leak in a blood vessel ? Name the component of blood which helps in this process and state how this component perform this function. OR (b) (i) The transport system in plants is relatively slower than in animals. Give reasons. (ii) State the role of phloem in the transport of materials in plants.
An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm. Use lens formula to find the position of the image formed in this case.
(a) A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed. OR (b) Define electric power. When do we say that the power consumed in an electric circuit is 1 watt ?
"Excessive use of chemicals and pesticides in agriculture adversely effect the environment." Justify this statement.
(a) "Displacement reactions also play a key role in extracting metals in the middle of the reactivity series." Justify this statement with two examples. (b) Why can metals high up in the reactivity series not be obtained by reduction of their oxides by carbon ?
(a) With the help of an activity, explain the conditions under which iron articles get rusted. OR (b) (i) Name two metals which react violently with cold water. List any three observations which a student notes when these metal are dropped in a beaker containing water. (ii) Write a test to identify the gas evolved (if any) during the reaction of these metals with water.
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Model answer · Conditions for rusting of iron
- 1.Iron articles get rusted only when they are exposed to both air and water. An activity shows this. Take three test tubes and place clean iron nails in each of them. Label these test tubes A, B and C. Pour some water in test tube A and cork it. Pour boiled distilled water in test tube B, add about 1 mL of oil and cork it. The oil will float on water and prevent the air from dissolving in the water. Put some anhydrous calcium chloride in test tube C and cork it. Anhydrous calcium chloride will absorb the moisture, if any, from the air. Leave the test tubes for a few days. The iron nails rust in test tube A, where they have both air and water. They do not rust in test tube B, where they have only water, or in test tube C, where they have only dry air.3 marks
- Begin with the direct answer: "Iron articles get rusted only when they are exposed to both air and water".
- Write why each test tube is set up as it is: "The oil will float on water and prevent the air from dissolving in the water" and "Anhydrous calcium chloride will absorb the moisture, if any, from the air".
- Write the observation for all three test tubes: the nails rust in test tube A but not in test tubes B and C.
Marks split as in the board’s published marking scheme
29. Plants have neither a nervous system nor muscles, even then they respond to stimuli. For example, the leaves of chhui-mui (touch-me-not) plant when touched begin to fold up and droop. (a) How is the information communicated in "touch-me-not" plants ? (b) What enables the plant cells to bring out the observable response ? (c) Differentiate the movement mentioned above from the movement of tendrils in a pea plant.
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Model answer · Movement in plants, touch-me-not
- 1.(a) In the touch-me-not plant, the leaves move at a point different from the point of touch. So the information that a touch has occurred must be communicated. The plant cells use electrical-chemical means to convey this information from cell to cell.1 mark
- 2.(b) Plant cells change shape by changing the amount of water in them. This causes swelling or shrinking, so the cells change shape and the leaves fold up and droop.1 mark
- 3.(c) Touch-me-not leaves: the movement is independent of growth; Pea tendrils: the movement is dependent on growth. Touch-me-not leaves: the movement does not take place in the direction of the stimulus; Pea tendrils: the movement takes place in the direction of the stimulus (tropic movement).1 mark
- In (a), write "electrical-chemical means" and say that the information is conveyed "from cell to cell".
- In (b), write "changing the amount of water in them" together with "swelling or shrinking".
- In (c), write each difference as a pair on one line, such as "independent of growth" against "dependent on growth".
Marks split as in the board’s published marking scheme
30. (a) What are chromosomes ? (b) Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms ?
How the model answer begins
1. (a) Chromosomes are thread-like structures in the nucleus, made of DNA and protein, which carry the genetic information passed from parents to offspring.
The full answer from Medha Ma’am →31. Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when the object is placed (i) at infinity and (ii) between infinity and pole P of the mirror.
32. Consider the following electric circuit : [Circuit Diagram] Calculate the values of the following : (a) The total resistance of the circuit (b) The total current drawn from the source (c) Potential difference across the parallel combination of 10 ohm and 15 ohm resistors
33. (a) Write the relationship between resistivity and resistance of a cylindrical conductor of length l and area of cross-section A. Hence derive the SI unit of resistivity. (b) Why are alloys used in electrical heating devices ?
How the model answer begins
1. (a) The resistance of a conductor is directly proportional to its length and inversely proportional to its area of cross-section: R = ρl/A, where ρ is the resistivity of the material.
The full answer from Medha Ma’am →(a) (i) Draw two isomeric structures of Butene (C4H8). (ii) Name the following compounds : (I) H-C-C-C-Cl (with H atoms) (II) H-C-C-C-C-H (with H and O atoms) (iii) Write the chemical equations for the following reactions. Mention one essential condition each for these reactions to take place. (I) Ethanol undergoes complete oxidation (II) Propene undergoes hydrogenation (III) Ethanoic acid reacts with ethanol OR (b) (i) A carbon compound X is a good solvent. On reaction with sodium, X forms two products Y and Z. Z is used to convert vegetable oil into vegetable ghee. Identify and name X, Y and Z. Also write the equation of reaction of X with sodium to justify your answer. (ii) Write chemical equation to show what happens when ethanol : (I) burns in oxygen/air. (II) is heated at 443 K in excess conc. H2SO4. (III) reacts with acidified potassium dichromate.
How the model answer begins
1. (a)(i) But-1-ene CH₂=CH–CH₂–CH₃ and but-2-ene CH₃–CH=CH–CH₃. OR (b)(i) X is ethanol (C₂H₅OH) and Y is sodium ethoxide (C₂H₅ONa).
The full answer from Medha Ma’am →(a) (i) Write the functions of the following parts of human female reproductive system : (I) Ovary (II) Fallopian tube (III) Uterus (ii) State briefly two contraceptive methods used by human males. OR (b) (i) Differentiate between self-pollination and cross-pollination. (ii) Identify A, B and C in the diagram given below and write one function of each.
(a) (i) The power of a lens 'X' is - 2.5 D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens ? (ii) "The value of magnification 'm' for a lens is - 2." Using new Cartesian Sign Convention and considering that an object is placed at a distance of 20 cm from the optical centre of this lens, state : (I) the nature of the image formed; (II) size of the image compared to the size of the object; (III) position of the image, and (IV) sign of the height of the image. (iii) The numerical values of the focal lengths of two lenses A and B are 10 cm and 20 cm respectively. Which one of the two will show higher degree of convergence/divergence ? Give reason to justify your answer. OR (b) (i) Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass. (ii) State Snell's law of refraction of light. (iii) Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of : (I) object distance, and (II) magnification.
How the model answer begins
1. (a)(i) The power is negative, so X is a concave (diverging) lens; it is prescribed to correct myopia (near-sightedness). OR (b)(i) Ray diagram: the ray falling obliquely from air enters the glass slab and bends towards…
The full answer from Medha Ma’am →[passage] (a) Write balanced chemical equations to show the products formed during electrolysis of brine. 1 (b) List two uses of any one product obtained during electrolysis of brine. 1 (c) (i) A mild non-corrosive basic salt 'A', used for faster cooking, is strongly heated to produce a compound 'B', that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated. 2 OR (c) (ii) Define water of crystallisation. Give two examples of salts that have water of crystallisation. 2
How the model answer begins
1. (a) 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g): chlorine at the anode, hydrogen at the cathode and sodium hydroxide solution near the cathode.
The full answer from Medha Ma’am →The maintenance functions of all living organisms must go on even when they are not doing anything particular. Even when we are just sitting in a class or even asleep, this maintenance job has to go on. These maintenance processes require energy to prevent damage and break-down of cells and tissues, which is obtained by the individual organism from the food prepared by the autotrophs, called producers. (a) Name and define the process by which green plants prepare food. (b) Write chemical equation involved in the above process. (c) (i) State in proper sequence the events that occur in synthesis of food by desert plants. OR (c) (ii) Explain giving reasons what happens to the rate at which the green plants will prepare food (I) during cloudy weather, and (II) when stomata get blocked due to dust.
How the model answer begins
1. (a) Green plants prepare food by photosynthesis.
The full answer from Medha Ma’am →In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is 220 V. (a) Write the colours of the insulation covers of the line wires through which supply comes to our homes. (b) What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated ? (c) (i) What is the function of the earth wire ? State the advantage of the earth wire in domestic electric appliances such as electric iron. OR (c) (ii) List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.
How the model answer begins
1. The line wires through which supply comes to our homes have two wires, the live wire and the neutral wire, with a potential difference of 220 V between them. The insulation cover of the live wire is of red colour and…
The full answer from Medha Ma’am →
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