CBSE Class 10 · Science · board exam 2027
CBSE Class 10 Science Question Paper 2024
The board’s 2024 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 11 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)
When 2 mL of sodium hydroxide solution is added to few pieces of granulated zinc in a test tube and then warmed, the reaction that occurs can be written in the form of a balanced chemical equation as :
- (A) NaOH + Zn -> NaZnO2 + H2O
- (B) 2NaOH + Zn -> Na2ZnO2 + H2 ✓
- (C) 2NaOH + Zn -> NaZnO2 + H2
- (D) 2NaOH + Zn -> Na2ZnO2 + H2O
Answer (the board’s key): (B)
Select from the following a decomposition reaction in which source of energy for decomposition is light :
- (A) 2FeSO4 -> Fe2O3 + SO2 + SO3
- (B) 2H2O -> 2H2 + O2
- (C) 2AgBr -> 2Ag + Br2 ✓
- (D) CaCO3 -> CaO + CO2
Answer (the board’s key): (C)
A metal and a non-metal that exists in liquid state at the room temperature are respectively :
- (A) Bromine and Mercury
- (B) Mercury and Iodine
- (C) Mercury and Bromine ✓
- (D) Iodine and Mercury
Answer (the board’s key): (C)
Carbon compounds : (i) are good conductors of electricity. (ii) are poor conductors of electricity. (iii) have strong forces of attraction between their molecules. (iv) have weak forces of attraction between their molecules. The correct statements are :
- (A) (i) and (ii)
- (B) (ii) and (iii)
- (C) (ii) and (iv) ✓
- (D) (i) and (iii)
Answer (the board’s key): (C)
Consider the following compounds : FeSO4 ; CuSO4 ; CaSO4 ; Na2CO3. In which of these compounds, the number of water molecules of crystallization in one formula unit is maximum?
- (A) FeSO4
- (B) CuSO4
- (C) CaSO4
- (D) Na2CO3 ✓
Answer (the board’s key): (D)
Oxides of aluminium and zinc are :
- (A) Acidic
- (B) Basic
- (C) Amphoteric ✓
- (D) Neutral
Answer (the board’s key): (C)
MnO2 + 4HCl -> MnCl2 + 2H2O + Cl2 The reaction given above is a redox reaction because in this case :
- (A) MnO2 is oxidised and HCl is reduced.
- (B) HCl is oxidised.
- (C) MnO2 is reduced.
- (D) MnO2 is reduced and HCl is oxidised. ✓
Answer (the board’s key): (D)
Consider the following statements : (i) The sex of a child is determined by what it inherits from the mother. (ii) The sex of a child is determined by what it inherits from the father. (iii) The probability of having a male child is more than that of a female child. (iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote. The correct statements are :
- (A) (i) and (iii)
- (B) (ii) and (iv) ✓
- (C) (iii) and (iv)
- (D) (i), (iii) and (iv)
Answer (the board’s key): (B)
Chromosomes : (i) carry hereditary information from parents to the next generation. (ii) are thread like structures located inside the nucleus of an animal cell. (iii) always exist in pairs in human reproductive cells. (iv) are involved in the process of cell division. The correct statements are :
- (A) (i) and (ii)
- (B) (iii) and (iv)
- (C) (i), (ii) and (iv)
- (D) (i) and (iv) ✓
Answer (the board’s key): (D)
In a nerve cell, the site where the electrical impulse is converted into a chemical signal is known as :
- (A) Axon
- (B) Dendrites
- (C) Neuromuscular junction ✓
- (D) Cell body
Answer (the board’s key): (C)
A stomata closes when : (i) it needs carbon dioxide for photosynthesis. (ii) it does not need carbon dioxide for photosynthesis. (iii) water flows out of the guard cells. (iv) water flows into the guard cells. The correct reason(s) in this process is/are :
- (A) (i) only
- (B) (i) and (iii)
- (C) (ii) and (iii) ✓
- (D) (ii) and (iv)
Answer (the board’s key): (C)
At what distance from a convex lens should an object be placed to get an image of the same size as that of the object on a screen ?
- (A) Beyond twice the focal length of the lens.
- (B) At the principal focus of the lens.
- (C) At twice the focal length of the lens. ✓
- (D) Between the optical centre of the lens and its principal focus.
Answer (the board’s key): (C)
The lens system of human eye forms an image on a light sensitive screen, which is called as :
- (A) Cornea
- (B) Ciliary muscles
- (C) Optic nerves
- (D) Retina ✓
Answer (the board’s key): (D)
The pattern of the magnetic field produced inside a current carrying solenoid is :
- (A) ✓
- (B)
- (C)
- (D)
Answer (the board’s key): (A)
Identify the food chain in which the organisms of the second trophic level are missing :
- (A) Grass, goat, lion
- (B) Zooplankton, Phytoplankton, small fish, large fish
- (C) Tiger, grass, snake, frog ✓
- (D) Grasshopper, grass, snake, frog, eagle
Answer (the board’s key): (C)
In which of the following organisms, multiple fission is a means of asexual reproduction ?
- (A) Yeast
- (B) Leishmania
- (C) Paramoecium
- (D) Plasmodium ✓
Answer (the board’s key): (D)
Assertion (A) : When zinc reacts with nitric acid, hydrogen gas is not evolved. Reason (R) : Nitric acid oxidises the hydrogen gas produced in the reaction to water and itself gets reduced.
- (A) Assertion (A) and Reason (R) are both correct and Reason (R) is the correct explanation of Assertion (A). ✓
- (B) Assertion (A) and Reason (R) are both correct but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is correct but Reason (R) is incorrect.
- (D) Assertion (A) is incorrect but Reason (R) is correct.
Answer (the board’s key): (A)
Assertion (A) : The accumulation of harmful chemicals is maximum in the organisms at the highest trophic level of a food chain. Reason (R) : Harmful chemicals are sprayed on crops to protect them from diseases and pests.
- (A) Assertion (A) and Reason (R) are both correct and Reason (R) is the correct explanation of Assertion (A).
- (B) Assertion (A) and Reason (R) are both correct but Reason (R) is not the correct explanation of Assertion (A). ✓
- (C) Assertion (A) is correct but Reason (R) is incorrect.
- (D) Assertion (A) is incorrect but Reason (R) is correct.
Answer (the board’s key): (B)
Assertion (A) : The rate of breathing in aquatic organisms is much faster than in terrestrial organisms. Reason (R) : The amount of oxygen dissolved in water is very high as compared to the amount of oxygen in air.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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) : The rainbow is a natural spectrum of sunlight in the sky. Reason (R) : Rainbow is formed in the sky when the sun is overhead and water droplets are also present in air.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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)
Section B · Written questions (19)
Name the type of chemical reaction in which calcium oxide reacts with water. Justify your answer by giving balanced chemical equation for the chemical reaction.
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Model answer · Combination reaction, quick lime
- 1.The reaction of calcium oxide (quick lime) with water is a combination reaction. A reaction in which a single product is formed from two or more reactants is known as a combination reaction.1 mark
- 2.Justification: two reactants, calcium oxide and water, combine to form a single product, calcium hydroxide (slaked lime), and a large amount of heat is released. CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat (Quick lime) (Slaked lime)1 mark
Marks split as in the board’s published marking scheme
State one role of each of the following in human digestive system : (i) Hydrochloric acid (ii) Villi (iii) Anal Sphincter (iv) Lipase
(A) How is the movement of leaves of a sensitive plant different from the downward movement of the roots ? OR (B) There is a hormone which regulates carbohydrate, protein and fat metabolism in our body. Name the hormone and the gland which secretes it. Why is it important for us to have iodised salt in our diet?
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Model answer · Plant movements, touch and gravity
- 1.The two movements differ first in their stimulus. Leaves of the sensitive plant: the stimulus is touch, and the movement is very quick. Downward movement of roots: the stimulus is gravity, the pull of the earth. This is called geotropism.1 mark
- 2.Leaves of the sensitive plant: no growth is involved in the movement; Roots: growth is involved in the movement. Leaves of the sensitive plant: the movement is non-directional; Roots: the movement is directional, or tropic, because roots always grow downwards.1 mark
- Name both stimuli: "touch" for the sensitive plant and "gravity" for the roots.
- Give both differences as pairs on separate lines: "no growth is involved" against "growth is involved", and "non-directional" against "directional".
Marks split as in the board’s published marking scheme
An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position of the image formed by the mirror.
(A) Show how you would connect three resistors each of resistance 6 Ω, so that the combination has a resistance of 9 Ω. Also justify your answer. OR (B) In the given circuit calculate the power consumed in watts in the resistor of 2 Ω :
(i) Two magnetic field lines do not intersect each other. Why ? (ii) How is a uniform magnetic field in a given region represented ? Draw a diagram in support of your answer.
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Model answer · properties of magnetic field lines
- 1.(i) If two field lines crossed, the field at that point would have two directions, which is impossible — the field at any point has only one direction (a compass needle there points one way).1 mark
- 2.(ii) A uniform magnetic field is represented by equally spaced, parallel straight lines.0.5 marks
- 3.Diagram: equally spaced parallel straight lines, each with an arrow pointing the same way.0.5 marks
Diagram: Draw four or five parallel, straight, equally spaced lines, each with an arrowhead pointing the same way. Label them "uniform magnetic field".
Marks split as in the board’s published marking scheme
Write one chemical equation each for the chemical reaction in which the following have taken place : (i) Change in colour (ii) Change in temperature (iii) Formation of precipitate Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.
(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste ? Give reason to justify your answer. (ii) How do we differentiate between a strong acid and a weak base in terms of ion-formation in aqueous solutions ? (iii) The acid rain can make the survival of aquatic animals difficult. How ?
(i) Why is respiratory pigment needed in multicellular organisms with large body size ? (ii) Give reasons for the following : (a) Rings of cartilage are present in the throat. (b) Lungs always contain a residual volume of air. (c) The diaphragm flattens and ribs are lifted up when we breathe in. (d) Walls of alveoli contain an extensive network of blood vessels.
How the model answer begins
1. (i) Respiratory pigment is needed because when the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body.
The full answer from Medha Ma’am →Define reflex action. With the help of a flow chart show the path of a reflex action such as sneezing.
How the model answer begins
1. A reflex action is a quick, involuntary and automatic response to a stimulus, made without thinking. Its pathway (reflex arc) passes through the spinal cord or, for reflexes of the head such as sneezing, the medulla of…
The full answer from Medha Ma’am →Study the diagram given below and answer the questions that follow : (i) Name the defect of vision represented in the diagram. Give reason for your answer. (ii) List two causes of this defect. (iii) With the help of a diagram show how this defect of vision is corrected.
How the model answer begins
1. The defect is hypermetropia (far-sightedness). Reason: the rays from a nearby object at N′ meet at a point behind the retina, so the image is formed behind the retina; the near point of the eye has moved farther away,…
The full answer from Medha Ma’am →Name and state the rule to determine the direction of a : (i) magnetic field produced around a current carrying straight conductor. (ii) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
How the model answer begins
1. (i) The direction of the magnetic field produced around a current-carrying straight conductor is given by the right-hand thumb rule.
The full answer from Medha Ma’am →(A) Plants -> Deer -> Lion In the given food chain, what will be the impact of removing all the organisms of second trophic level on the first and third trophic level? Will the impact be the same for the organisms of the third trophic level in the above food chain if they were present in a food web? Justify. OR (B) A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function. Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?
How the model answer begins
1. If all the deer, the organisms of the second trophic level (herbivores), are removed, the number of plants, the organisms of the first trophic level (producers), will increase, because no herbivores are left to eat them.
The full answer from Medha Ma’am →(A) (i) Define a homologous series of carbon compounds. (ii) Why is the melting and boiling points of C4H8 higher than that of C3H6 or C2H4 ? (iii) Why do we NOT see any gradation in chemical properties of a homologous series compounds ? (iv) Write the name and structures of (i) aldehyde and (ii) ketone with molecular form C3H6O. OR (B) (i) Write the name and structure of an organic compound 'X' having two carbon atoms in its molecule and its name is suffixed with '-ol'. (ii) What happens when 'X' is heated with excess concentrated sulphuric acid at 443 K? Write chemical equation for the reaction stating the conditions for the reaction. Also state the role played by concentrated sulphuric acid in the reaction. (iii) Name and draw the electron dot structure of hydrocarbon produced in the above reaction.
How the model answer begins
1. (A) (i) A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain. This means the same functional group is attached to carbon chains of different…
The full answer from Medha Ma’am →35. (A) (i) Name three techniques/devices used by human females to avoid pregnancy. Mention the side effects caused by each. (ii) What will happen if in a human female (a) fertilisation takes place, (b) an egg is not fertilised ? OR (B) (i) Draw a diagram showing spore formation in Rhizopus and label the (a) reproductive and (b) non-reproductive parts. Why does Rhizopus not multiply on a dry slice of bread ? (ii) Name and explain the process by which reproduction takes place in Hydra.
How the model answer begins
1. (A)(i) Barrier methods such as the condom or diaphragm; side effect: occasional irritation or allergy, and failure if torn. OR (B)(i) Diagram: thread-like hyphae on the bread, with erect stalks ending in round sporangia…
The full answer from Medha Ma’am →36. (A) (i) Define electric power. Express it in terms of potential difference (V) and resistance (R). (ii) An electric oven is designed to work on the mains voltage of 220 V. This oven consumes 11 units of electrical energy in 5 hours. Calculate : (a) power rating of the oven (b) current drawn by the oven (c) resistance of the oven when it is red hot OR (B) (i) Write the relation between resistance R and electrical resistivity ρ of the material of a conductor in the shape of cylinder of length l and area of cross-section A. Hence derive the SI unit of electrical resistivity. (ii) The resistance of a metal wire of length 3 m is 60 Ω. If the area of cross-section of the wire is 4x10^-7 m^2, calculate the electrical resistivity of the wire. (iii) State how would electrical resistivity be affected if the wire (of part ‘ii’) is stretched so that its length is doubled. Justify your answer.
How the model answer begins
1. (i) Electric power is the rate at which electric energy is dissipated or consumed in an electric circuit. Its SI unit is watt (W).
The full answer from Medha Ma’am →37. The metals produced by various reduction processes are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining. (i) What is the cathode and anode made of in the refining of copper by this process ? (ii) Name the solution used in the above process and write its formula. (iii) (A) How copper gets refined when electric current is passed in the electrolytic cell ? OR (iii) (B) You have two beakers ‘A’ and ‘B’ containing copper sulphate solution. What would you observe after about 2 hours if you dip a strip of zinc in beaker ‘A’ and a strip of silver in beaker ‘B’? Give reason for your observations in each case.
How the model answer begins
1. (i) In the electrolytic refining of copper, the cathode is made of pure copper: a thin strip of pure copper is used as the cathode.
The full answer from Medha Ma’am →Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance. (i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce F1 progeny, which two observations were made by him in F1 plants? (ii) Write one difference between dominant and recessive trait. (iii) (A) In a cross with two pairs of contrasting characters RRYY X rryy (Round Yellow) (Wrinkled Green) Mendel observed 4 types of combinations in F2 generation. By which method did he obtain F2 generation ? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment. OR (iii) (B) Justify the statement : "It is possible that a trait is inherited but may not be expressed."
How the model answer begins
1. (i) When a pure tall pea plant was crossed with a pure short pea plant, all plants in the F1 progeny were tall. No short plants were seen.
The full answer from Medha Ma’am →39. Study the data given below in which focal length and relative distance of the object placed in front of three concave mirrors A, B and C are given : Case | Mirror | Focal length (cm) | Object-distance (cm) 1 | A | 20 | 45 2 | B | 15 | 30 3 | C | 30 | 20 (i) In which of the above cases will the size of the image formed by the mirror be smaller than the size of the object? Justify your answer. (ii) List two properties of the image formed in case 2. (iii) (A) What is the nature and size of the image formed by mirror C? Draw a ray diagram to justify your answer. OR (iii) (B) An object is placed at a distance of 18 cm from the pole of a concave mirror of focal length 12 cm. Find the position of the image in this case.
How the model answer begins
1. (i) The image is smaller than the object in Case 1, which is mirror A.
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