Class 10th CBSE Complete Science Mid-Term Marathon 2026: Important Numericals & Concepts to Practise Before the Exam

Reading a Science chapter can feel manageable until it is time to solve questions. A Physics numerical may require a formula that is easy to forget, a Chemistry question may ask for a reaction type instead of the equation, and a Biology question may require a process to be explained in the correct sequence. These gaps can cost marks even when the concepts seem familiar.

To bridge these gaps, PW is providing the Class 10 Science Half Mid-Term Marathon 2026, covering important concepts, numericals, reactions, processes and application-based questions from Physics, Chemistry and Biology. The marathon helps you revise the concepts first and then understand how to apply them while solving exam-style questions.

Important Class 10 Science Concepts to Revise Before the Half Mid-Term

The Class 10 Science Half Mid-Term 2026 requires revision of concepts across Physics, Chemistry and Biology. Focus first on the key topics below, including formulas, reactions, processes and important applications, before moving to question practice. 

Chemistry: Reactions, Acids, Bases and Salts

Physics: Light, Human Eye and Atmospheric Phenomena

Biology: Life Processes, Control and Coordination and Reproduction

Class 10 Science Important Questions to Practise

Once the concepts are revised, attempt the following questions without checking the answers. These questions cover the major question types included in the PW Science Marathon.

Chemistry Most Important Questions

Chemical Reactions and Equations

1. Balance the following chemical equation:

Al₂O₃ + HCl → AlCl₃ + H₂O

What are the values of the coefficients?

A. 1, 6, 2, 3
B. 1, 6, 3, 2
C. 2, 6, 2, 3
D. 2, 6, 3, 2

Answer: A. 1, 6, 2, 3.

2. Find the ratio of reactants in the balanced equation:

xFe + yH₂O → Fe₃O₄ + 4H₂

A. 2:3
B. 3:4
C. 1:4
D. 4:1

Answer: B. 3:4.

3. Identify the endothermic reactions.

P) Photosynthesis
Q) Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O
R) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
S) CaCO₃ → CaO + CO₂

A. Only P
B. Only S
C. Only Q and R
D. Only P and S

Answer: D. Only P and S.

4. Which of the following are exothermic processes?

(i) Reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor

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

Answer: A. (i) and (ii).

5. What are the main observations when magnesium ribbon burns in air?

(i) It burns with a dazzling white flame.
(ii) A white powder is formed.
(iii) The ribbon vapourises.
(iv) The aqueous solution of the white powder turns blue litmus to...

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

Answer: C. (i) and (ii).

6. Which are examples of thermal decomposition?

(i) 2AgCl → 2Ag + Cl₂
(ii) CaCO₃ → CaO + CO₂
(iii) 2H₂O₂ → H₂ + O₂
(iv) 2KClO₃ → 2KCl + 3O₂

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

Answer: D. (ii) and (iv).

7. Assertion and Reason

Assertion (A): Decomposition reactions are generally endothermic reactions.

Reason (R): Decomposition of organic matter into compost is an exothermic process.

A. Both A and R are true, and R correctly explains A
B. Both A and R are true, but R does not correctly explain A
C. A is true, but R is false
D. A is false, but R is true

Answer: B. Both A and R are true, but R does not correctly explain A.

8. Identify the reducing agent:

2Na + 2H₂O → 2NaOH + H₂

A. Na
B. H₂O
C. NaOH
D. H₂

Answer: A. Na.

9. Identify the correct statement:

CuO + H₂ → Cu + H₂O

A. CuO is oxidised and H₂ is reduced.
B. H₂ is oxidised and CuO is reduced.
C. CuO is a reducing agent.
D. H₂ is an oxidising agent.

Answer: B. H₂ is oxidised and CuO is reduced.

10. Why is the following a redox reaction?

MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂

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: D. MnO₂ is reduced, and HCl is oxidised.

11. Identify X, Y and Z.

A substance X is a metal oxide. It reacts with water to form Y, whose solution is used for whitewashing. Y reacts slowly with carbon dioxide to form Z, which is commonly called marble, chalk or limestone.

Answer:

X: Calcium oxide, CaO
Y: Calcium hydroxide, Ca(OH)₂
Z: Calcium carbonate, CaCO₃

12. What happens in these chemical changes?

(i) Heating calcium carbonate in the absence of oxygen

(ii) Heating lead nitrate powder

(iii) Heating green ferrous sulphate crystals

(iv) Passing electricity through acidulated water

(v) Putting silver chloride or silver bromide in sunlight

Answer:

(i) Calcium carbonate:

CaCO₃ → CaO + CO₂

This is thermal decomposition.

(ii) Lead nitrate:

2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

A yellow residue of lead oxide and brown nitrogen dioxide fumes are produced.

(iii) Ferrous sulphate:

2FeSO₄ → Fe₂O₃ + SO₂ + SO₃

The green crystals first lose water of crystallisation and then decompose on further heating.

(iv) Acidulated water:

2H₂O → 2H₂ + O₂

Hydrogen is produced at the cathode and oxygen at the anode in a 2:1 volume ratio.

(v) Silver chloride and silver bromide:

2AgCl → 2Ag + Cl₂

2AgBr → 2Ag + Br₂

These are photolytic decomposition reactions.

13. Write balanced equations and identify the reaction type.

(i) Lead nitrate + potassium iodide

(ii) Sodium sulphate + barium chloride

(iii) Silver nitrate + sodium chloride

(iv) Hydrogen sulphide + copper sulphate

Answer:

All four are double displacement or precipitation reactions.

(i) Pb(NO₃)₂ + 2KI → PbI₂↓ + 2KNO₃

A yellow precipitate of lead iodide is formed.

(ii) Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

A white precipitate of barium sulphate is formed.

(iii) AgNO₃ + NaCl → AgCl↓ + NaNO₃

A white precipitate of silver chloride is formed.

(iv) CuSO₄ + H₂S → CuS↓ + H₂SO₄

A black precipitate of copper sulphide is formed.

Acids, Bases and Salts

14. Which acid is present in nettle sting?

A. Acetic acid
B. Methanoic acid
C. Tartaric acid
D. Citric acid

Answer: B. Methanoic acid.

15. Which acid is present in tomato?

A. Methanoic acid
B. Acetic acid
C. Lactic acid
D. Oxalic acid

Answer: D. Oxalic acid.

16. Which statements about pH are correct?

(i) Higher the pH, stronger the acid.
(ii) Higher the pH, weaker the acid.
(iii) Lower the pH, stronger the base.
(iv) Lower the pH, weaker the base.

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

Answer: D. (ii) and (iv).

17. What is the product X formed from baking soda and tartaric acid that makes bread and cakes soft and spongy?

A. Carbon dioxide
B. Carbon monoxide
C. Sodium tartrate
D. Hydrogen

Answer: A. Carbon dioxide.

18. Which of the following represents a family of salts?

A. NaCl, Na₂SO₄, CaSO₄
B. K₂SO₄, Na₂SO₄, CaSO₄
C. NaNO₃, CaCO₃, Na₂CO₃
D. MgSO₄, CuSO₄, MgCl₂

Answer: B. K₂SO₄, Na₂SO₄, CaSO₄.

19. Arrange the following solutions in ascending order of pH.

A. Potassium nitrate
B. Ammonium chloride
C. Sodium carbonate

A. A < B < C
B. B < C < A
C. C < A < B
D. B < A < C

Answer: D. B < A < C.

Physics Most Important Questions

Light, Lenses and Human Eye

1. Solve the following lens numericals.

(a) Find the focal length of a lens having power −2.0 D. Identify the type of lens.

Solution:

P = 1/f

f = 1/−2

f = −0.5 m

Therefore,

f = −50 cm

The negative focal length shows that it is a concave or diverging lens.

(b) A lens has power +1.5 D. Calculate its focal length and state whether it is converging or diverging.

Solution:

f = 1/1.5

f ≈ 0.67 m

Therefore,

f ≈ +66.7 cm

The positive focal length shows that it is a convex or converging lens.

2. Why can a normal human eye not see clearly an object placed closer than 25 cm?

Solution:

The eye focuses on nearby objects by contracting the ciliary muscles. This makes the eye lens thicker and decreases its focal length.

However, the ciliary muscles can contract only up to a certain limit. Once this limit is reached, the lens cannot become sufficiently thick to focus on an object placed closer than 25 cm.

Therefore, 25 cm is considered the near point of a normal human eye.

3. What is hypermetropia? Explain its causes and correction. A hypermetropic eye has a near point of 1 m. What type of lens is required to correct it?

Solution:

Hypermetropia or long-sightedness is a defect in which a person can see distant objects clearly but cannot see nearby objects distinctly.

It can occur because:

• The converging power of the eye lens is too low.

• The eyeball is shorter than normal.

A convex lens is used to correct hypermetropia because it provides additional converging power and helps the image form on the retina.

4. Explain scattering of light.

Answer the following:

(a) Why does the sky appear blue?

(b) Why does the Sun appear reddish at sunrise and sunset?

(c) Why does the sky appear dark to an astronaut in space?

Solution:

Scattering of light occurs when light is redirected in different directions by tiny particles present in a medium.

(a) Blue sky:

Blue light is scattered more strongly by atmospheric particles and reaches our eyes from different directions. Hence, the sky appears blue.

(b) Reddish Sun:

At sunrise and sunset, sunlight travels through a longer distance in the atmosphere. Most shorter wavelengths are scattered away, while more red light reaches our eyes.

(c) Dark sky in space:

Space has almost no atmosphere and therefore very few particles to scatter sunlight. Hence, the sky appears dark or black to an astronaut.

For more questions and detailed explanations, refer to the PW Class 10 Science Half Mid-Term Marathon 2026 video. The lecture can help you revise the concepts covered in the marathon and understand how the questions are solved

Biology Most Important Questions

Life Processes, Coordination and Reproduction

1. Give two reasons why absorption of digested food takes place mainly in the small intestine.

Solution:

The small intestine is specialised for absorption because:

• It contains numerous villi and microvilli, which provide a large surface area.

• The villi have a rich blood supply, which helps transport absorbed nutrients throughout the body.

2. Which substance will not be selectively reabsorbed during urine formation?

A. Glucose
B. Amino acids
C. Water
D. Urea

Answer: D. Urea.

3. Which hormone controls phototropic and geotropic responses in plants?

A. Auxin
B. Gibberellins
C. Cytokinin
D. Ethylene

Answer: A. Auxin.

4. What is formed when glucose breaks down in muscle cells in the absence of sufficient oxygen?

A. Ethanol + CO₂ + energy
B. Lactic acid + energy
C. Lactic acid + CO + energy
D. CO₂ + water + energy

Answer: B. Lactic acid + energy.

5. Why is iodised salt advisable? Name the disease caused by iodine deficiency and state one symptom.

Solution:

Iodised salt is recommended because iodine is required for the production of thyroxine, a hormone involved in regulating metabolism.

Iodine deficiency can cause goitre, which involves enlargement of the thyroid gland.

One symptom: Swelling or enlargement of the neck.

How Can the PW Class 10 Science Mid-Term Marathon Help With Revision?

The PW Mid-Term Marathon brings concepts and question practice together, making it easier to identify what needs another round of revision before the exam. You can use the lectures to:

• Refresh Difficult Concepts: Revisit topics that you remember only partially instead of rereading every chapter from the beginning.

• Practise Application-Based Questions: Work through questions where you need to apply a formula, identify a reaction, explain a process or interpret a situation.

• Revise Science Numericals: Practise Physics questions involving lens power, focal length and other formula-based applications.

• Strengthen Diagrams and Processes: Revise important Biology diagrams and processes alongside their functions and explanations.

• Improve Answer Writing: Observe how conceptual and reasoning-based questions can be approached step by step.

• Identify Weak Areas: Use the questions above as a self-test and return to the marathon for concepts where you make repeated mistakes.

The ideal way to prepare for a Class 10 Science half mid-term is to combine concept revision with question practice. Revise the key ideas, solve the questions without looking at the answers and use the PW Marathon to revisit topics where you need more clarity.