CBSE Board Class 10 Science Question Paper 2025 Set 3 (31-6-3) Available- Download Solution PDF with Answer Key

Example of thermal decomposition reaction are:

(i) \( 2 \, AgCl \rightarrow 2 \, Ag + Cl_2 \)

(ii) \( CaCO_3 \rightarrow CaO + CO_2 \)

(iii) \( 2 \, H_2O \rightarrow 2 \, H_2 + O_2 \)

(iv) \( 2 \, KClO_3 \rightarrow 2 \, KCl + 3 \, O_2 \)

• (A) (i) and (ii)
• (B) (ii) and (iii)
• (C) (iii) and (iv)
• (D) (ii) and (iv)

You have three aqueous solutions A, B and C as given below:

A - Potassium nitrate

B - Ammonium chloride

C - Sodium carbonate

The ascending order of the pH of these solutions is:

• (A) \( A < B < C \)
• (B) \( B < C < A \)
• (C) \( C < A < B \)
• (D) \( B < A < C \)

Which one of the following metals is protected from corrosion by a layer of its own oxide?

• (A) Aluminium
• (B) Copper
• (C) Silver
• (D) Gold

The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is:

• (A) Blue
• (B) Pale green
• (C) Yellow
• (D) Reddish brown

A Hydrocarbon which does not belong to the same homologous series of carbon compounds is:

• (A) \( C_4H_{10} \)
• (B) \( C_6H_{14} \)
• (C) \( C_7H_{14} \)
• (D) \( C_{10}H_{22} \)

The water of crystallization is present in:

(i) Bleaching Powder

(ii) Plaster of Paris

(iii) Washing Soda

(iv) Baking Soda

• (A) (ii) and (iv)
• (B) (ii) and (iii)
• (C) (i) and (iii)
• (D) (i) and (iv)

Juice of tamarind turns blue litmus to red. It is because of the presence of a chemical compound called:

• (A) Acetic acid
• (B) Methanoic acid
• (C) Oxalic acid
• (D) Tartaric acid

Electrical impulse travels in a neuron from:

• (A) Nerve ending \( \rightarrow \) Axon \( \rightarrow \) Cell body \( \rightarrow \) Dendrite
• (B) Dendrite \( \rightarrow \) Cell body \( \rightarrow \) Axon \( \rightarrow \) Nerve ending
• (C) Cell body \( \rightarrow \) Dendrite \( \rightarrow \) Axon \( \rightarrow \) Nerve ending
• (D) Dendrite \( \rightarrow \) Axon \( \rightarrow \) Nerve ending \( \rightarrow \) Cell body

A tall pea plant with round seeds (TTRR) is crossed with a short pea plant with wrinkled seeds (ttrr). The \( F_1 \) generation will be:

• (A) 25% tall with round seeds
• (B) 50% tall with wrinkled seeds
• (C) 75% tall with wrinkled seeds
• (D) 100% tall with round seeds

The basic filtration unit of the excretory system in human beings is:

• (A) Nephron
• (B) Urethra
• (C) Neuron
• (D) Urinary bladder

Which one of the following is not an excretory product in plants?

• (A) \(CO_2\)
• (B) Starch
• (C) Resins and gums
• (D) Dead cells

In human alimentary canal, the digestive juice secreted by the gastric glands are:

• (A) Bile, Trypsin, Pepsin
• (B) Hydrochloric acid, Pepsin, Mucus
• (C) Lipase, Bile, Mucus
• (D) Salivary amylase, Pepsin, Bile

The curvature of the eye lens of the human eye:

• (A) is fixed
• (B) can be increased
• (C) can be decreased
• (D) increases or decreases as the case may be

Identify from the following the ray diagram which shows the correct path of the reflected ray for the ray incident on a concave mirror as shown:

In the following groups of wastes, which group contains only non-biodegradable wastes?

• (A) Leather footwear, Plastic plate, Polythene bag
• (B) Empty medicine bottle, Milk packet, Aluminium can
• (C) Used tea leaves, Cardboard box, Iron nail
• (D) Plastic Syringes, Newspaper, Ball point pen

Consider the following food chain:

Grass \( \rightarrow \) Grasshopper \( \rightarrow \) Frog \( \rightarrow \) Snake \( \rightarrow \) Eagle

If the amount of energy available at third trophic level is 50 kJ, the available energy at the producer level was:

• (A) 0.5 kJ
• (B) 5 kJ
• (C) 500 kJ
• (D) 5000 kJ

Assertion (A): Xylem tissue moves water and minerals obtained from the soil by the roots.

Reason (R): Xylem tissue is found only in the roots of a plant.

• (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, and 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.

Assertion (A): Carbon and its compounds are our major sources of fuels.

Reason (R): Most of the carbon compounds on burning release a large amount of heat and light.

• (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, and 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.

Assertion (A): Food web is a network of several food chains operating in an ecosystem.

Reason (R): Food web decreases the stability of an ecosystem.

• (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, and 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.

Assertion (A): In the common domestic circuits, the earth wire is connected to a metallic plate buried deep inside the earth.

Reason (R): Earth wire ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, so the user may not get a severe electric shock.

• (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, and 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.

Question 21:

Name a metal found in the earth's crust:
(i) in free state and
(ii) in the form of its compound.

State where each of these metals are placed in the reactivity series of metals.

Out of the two media - Medium 1 and Medium 2, in which is the speed of light more?

(b) State the reason for the bending of the refracted ray away from the normal.

(c) Express the refractive index of Medium 2 with respect to Medium 1 in terms of the speed of light in both media.

(a) Give reasons:

(i) The sky appears dark to passengers flying at very high altitude.

(a) (ii) 'Danger' signal lights are red in colour.

(b) What is a rainbow? 'We see a rainbow in the sky only after the rainfall.' Why?

(a) "Proteins control the expression of various characters." Explain this statement by taking an example of "tallness" as a characteristic in plants.

(b) Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.

(a) How is the brain protected in our body?

(b) A doctor finds in one of his patients that he is not maintaining a proper posture and balance of his body. State the region of brain and also the part of brain which is responsible for it.

Write the percentage of the energy of sunlight captured by green plants, to convert it into food energy. Explain the fate of this energy when green plants are eaten by primary consumers.

Explain why respiration is considered an exothermic reaction. Give the chemical equation for this reaction.

(a) State the chemical property in each case on which the following uses of baking soda are based upon:

(i) As an antacid

(ii) As a constituent in making baking powder

(iii) In soda-acid fire extinguishers

(b) Write chemical equations to show what happens when an acid reacts with a:

(i) Metal

(ii) Base

(iii) Carbonate

Write the name of the main product formed in each case.

Question 29:
A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below:

Question 29:

(a) What is the focal length of the convex lens used? Give reason to justify your answer.

(b) Which one of the sets of observations is not correct and why?

(a) "In human beings the genes inherited from the parents decide whether the newborn individual is male or female." Explain this statement with the help of a flow diagram.

(b) "Some animals rely on environmental cues for sex determination." Justify this statement giving an example.

Name the blood vessel that brings (i) oxygenated blood (ii) deoxygenated blood to the human heart. Also name that chamber of the heart which receives deoxygenated blood and state how deoxygenated blood from this chamber is sent to lungs for oxygenation.

A person uses lenses of power -0.5 D in his spectacles for the correction of his vision.
(a) Name the defect of vision the person is suffering from.

(b) List two causes of this defect.

(c) Determine the focal length of the lenses used in the spectacles.

(a) Explain the statement "Potential difference between two points is 1 volt".

(b) What do the symbols given below represent in an electric circuit? Write one function of each.

(a) What are magnetic field lines? How is the direction of magnetic field at a point determined? Draw the pattern of magnetic field lines of the magnetic field produced by a current-carrying circular loop. Mark on it the direction of (i) current and (ii) magnetic field lines. Name the two factors on which the magnitude of the magnetic field due to a current-carrying coil depends.

(b) Why can't two magnetic field lines cross each other? Draw magnetic field lines showing the direction of the magnetic field due to a current-carrying long straight solenoid. State the conclusion which can be drawn from the pattern of magnetic field lines inside the solenoid. Name any two factors on which the magnitude of the magnetic field due to this solenoid depends.

(a) Name the method by which Amoeba and Leishmania reproduce. Write a major difference in the way they divide to produce new individuals.

(b) What is asexual reproduction? Explain the process of budding in Hydra.

(c) Give two methods used to grow rose and jasmine plants by vegetative propagation.

(a) Write one function each of the parts - (i) petals (ii) anther (iii) style and (iv) ovary of a bisexual flower.

(b) Give one example each of a unisexual flower and a bisexual flower. Mention the changes which a flower undergoes after fertilization.

(a) Name an alcohol and a carboxylic acid having two carbon atoms in their structures. Draw their structures and state how this alcohol can be converted into a carboxylic acid. What happens when these two compounds react in the presence of an acid? Write chemical equations for the reactions involved in the two cases mentioned above.

(b) What are soaps? Write the structure of a soap molecule. Explain the cleansing action of a soap. Why are soaps not considered suitable for washing clothes in a region where water is hard? How is this problem overcome?

(I) How does electrical conductivity and melting point of a metal change when it is converted to its alloy by mixing a small amount of an element in it?

(II) Name an alloy used for welding two wires together in an electric circuit. Write its major constituents.

(III) (a) What are alloys? How is 'Brass' (an alloy) prepared?

(III) (b) What is stainless steel? How is it prepared? Write one important property which makes it more useful in making cooking utensils as compared to its primary metal.

(I) Name the movement which causes 'X' and 'Y' to grow downwards and upwards respectively.

(II) Write the name of a hormone that plays a major role in (i) falling of leaves (ii) rapid cell division.

(III) (b) Name the plant hormone which is synthesized at the shoot tip. How does this hormone help the plant to bend towards light?

(I) Draw a circuit diagram showing the above two resistors X and Y joined in parallel with the same battery and same ammeter and voltmeter.

(II) In which combination of resistors will the (i) potential difference across X and Y and (ii) current through X and Y, be the same?

(III) (a) Find the current drawn from the battery by the series combination of the two resistors (X and Y).

(III) (b) Determine the equivalent resistance of the parallel combination of the two resistors (X and Y).