CBSE Class 10 Science Answer Key 2024 (Available): Detailed solutions PDF

1. Identify the product 'X' obtained in the following chemical reaction: CaCO ₃ → X + CO ₂

(A) Quick lime

2. Select a pair of natural indicator from the following:

(A) Litmus and methyl orange

3. A chemical compound used in glass, soap and paper industries is

(A) Washing Soda

4. The structural formula of Cyclohexane is

(B)

5. Consider the following Chemical equation :
a Al ₂ O ₃ + b HCl → c AlCl ₃ + d H ₂ O
In order to balance this chemical equation, the values of a, b, c and d must be

(A) 1, 6, 2 and 3

6. Which one of the following hydrocarbons is different from the others?

(B) C ₇ H ₁₄

7. Which one of the following reactions is different from the remaining three?

(B) CaO + H ₂ O → Ca(OH) ₂

8. Select from the following a plant hormone which promotes cell division?

(D) Cytokinins

9. Part(s) of a flower which attracts insects for pollination is (are)

(C) Petals only

10. In an experiment to study independent inheritance of two separate traits: shape and colour of seeds, the ratio of the different combinations in F ₂ progeny would be

(C) 9:3:3:1

11. Which of the following statement (s) is (are) true about human heart?
(a) Right atrium receives oxygenated blood from lungs through pulmonary artery.
(b) Left atrium transfers oxygenated blood to left ventricle which sends it to various parts of the body.
(c) Right atrium receives deoxygenated blood from different parts of the body through vena cava.
(d) Left atrium transfers oxygenated blood to aorta which sends it to different parts of the body.

(C) (b) and (c)

12. A cross between two tall pea plants resulted in offsprings having a few dwarf plants. The gene-combination of the parental plants must be

(A) Tt and Tt

13. The Phenomena of light involved in the formation of a rainbow in the sky are

(B) Refraction, dispersion and total internal reflection

14. In case of four wires of same material, the resistance will be minimum if the diameter and length of the wire respectively are

(A) D/2 and L/4

15. A food chain will be more advantageous in terms of energy if it has

(A) 2 trophic levels

16. Consider the following statements about ozone :
(a) Ozone is poisonous gas.
(b) Ozone shields the earth's surface from the infrared radiation from the sun.
(c) Ozone is a product of UV radiations acting on oxygen molecule-
(d) At the lower level of the earth's atmosphere, ozone performs most essential function.
The correct statements are

(B) (a) and (c)

1. Select from the following the conditions responsible for the rapid spread of bread mould on a slice of bread:
(i) Formation of large number of spores
(ii) Presence of moisture and nutrients in bread
(iii) Low temperature
(iv) Presence of hyphae

(A) (i) and (ii)

2. The incorrect statement about placenta is:

(C) It has a very small surface area for glucose and oxygen to pass from mother to the embryo.

3. An aqueous solution 'A' turns phenolphthalein solution pink. When another aqueous solution 'B' is added to the pink solution, the pink colour disappears. Now when a few drops of solution 'A' are added to this reaction, the mixture appears pink again. The respective changes in the nature of the solution are from:

(D) basic → acidic → basic

4. The correct sequence of events when someone's hand touches a hot object unconsciously:

(C) Receptors in skin → Sensory neuron → Relay neuron → Motor neuron → Effector muscle in arm

5. To balance the following chemical equation, the values of the coefficients x, y and z must be respectively:
x Zn(NO ₃ ) ₂ → y ZnO + zNO ₂ + O ₂

(C) 2, 2, 4

6. Which of the following is a redox reaction, but not a combination

(D) Fe ₂ O ₃ + 3CO ₂ → Fe + 3CO ₂

7. An aqueous solution of sodium chloride is prepared in distilled water. The pH of this solution is :

(C) 7

8. A metal 'X' is used in thermit process. When 'X' is heated with oxygen, it gives an oxide 'Y', which is amphoteric in nature. 'X' and 'Y' respectively are:

(B) Al, Al ₂ O ₃

9. The process in which transport of soluble products of photosynthesis takes place in plants is known as:

(D) Translocation

10. Sense organ in which olfactory receptors are present is :

(A) Nose

11. Which one of the following is not a natural ecosystem?

(D) Cropland ecosystem

12 .A uniform magnetic field exists in the plane of paper as shown in the diagram. In this field, an electron (e ^- ) and a positron (p ⁺ ) enter as shown. The electron and positron experience forces:

(A) both pointing into the plane of the paper.

13. How will the image formed by a convex lens be affected, if the upper half of the lens is wrapped with a black paper?

(C) The brightness of the image will reduce.

14. The phenomena of light involved in the formation of rainbow are :

(C) Reflection, dispersion and internal reflection

15. The colour of light for which the refractive index of glass is minimum, is:

(A) Red

16. The current carrying device which produces a magnetic field similar to that of a bar magnet is :

(C) A solenoid

17. Assertion (A): Electrons move from lower potential to higher potential in a conductor.
Reason (R): A dry cell maintains electric potential difference across the ends of a conductor.

(D) Assertion (A) is false, but Reason (R) is true.

18. Assertion (A): Some vegetable oils are healthy.
Reason (R): Vegetable oils generally have long unsaturated carbon chains.

(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

19. Assertion (A): Sex of the children will be determined by what they inherit from their mother.
Reason (R): Women have XX sex chromosomes.

(D) Assertion (A) is false, but Reason (R) is true.

20. Assertion (A): Green plants trap only 1% of the energy of sunlight that falls on their leaves.
Reason (R): All green plants are the producers in a food chain.

(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

(i) 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 :

(b) 2NaOH + Zn → Na ₂ ZnO ₂ + H ₂

(ii) Select from the following a decomposition reaction in which source of energy for decomposition is light :

(d) CaCO ₃ → CaO + CO ₂

(iii) A metal and a non-metal that exists in liquid state at the room temperature are respectively:

(c) Mercury and Bromine

(iv) Carbon compounds:
(i) are good conductors of electricity.
(ii) are bad 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:

(c) (ii) and (iv)

(v) Consider the following compounds : FeSO ₄ ; CuSO ₄ ; CaSO ₄ ; Na ₂ CO ₃
The compound having maximum number of water of crystallisation in its crystalline form in one molecule is :

(d) Na ₂ CO ₃

(vi) Oxides of aluminium and zinc are:

(c) amphoteric

(vii) MnO ₂ + 4HCl → MnCl ₂ + 2H ₂ O + Cl ₂
The reaction given above is a redox reaction because in this case:

(d) MnO ₂ is reduced and HCl is oxidised.

(viii) 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:

(b) (ii) and (iv)

(ix) 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:

(d) (i), (ii), and (iv)

(x) In a nerve cell, the site where the electrical impulse is converted into a chemical signal is known as:

(a) Axon

(xi) 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 :

(c) (ii) and (iii)

(xii) 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?

(c) At twice the focal length of the lens.

(xiii) The lens system of human eye forms an image on a light sensitive screen, which is called as:

(d) Retina

(xiv) The pattern of the magnetic field produced inside a current carrying solenoid is :

(a) parallel straight lines

(xv) Identify the food chain in which the organisms of the second trophic level are missing:

(c) Tiger, grass, snake, frog

(xvi) In which of the following organisms, multiple fission is a means of asexual reproduction?

(d) Plasmodium

(i) Assertion (A): Hydrogen gas is not evolved when zinc reacts with nitric acid.
Reason (R): Nitric acid oxidises the hydrogen gas produced to water and itself gets reduced.

(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

(ii) Assertion (A): 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 the crops to protect them from diseases and pests.

(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

(iii) 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.

(c) Assertion (A) is true, but Reason (R) is false.

(iv) 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).

CBSE 10th Science Exam Analysis 2024