CHAPTER -1 | Class 10TH Science

Part I: CBSE Board Level Questions

Section A: Multiple Choice Questions (MCQs)

1. Which of the following is a physical change?

(a) Burning of Magnesium ribbon in air
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Boiling of water to give water vapour
(d) Rusting of iron

Solution: (c)
Boiling of water is a physical change because the chemical composition of water remains the same.

2. What happens when dilute hydrochloric acid is added to iron fillings?

(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.

Solution: (a)

Fe + 2HCl → FeCl₂ + H₂

This is a displacement reaction.

3. The reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe is an example of a:

(a) Combination reaction
(b) Double displacement reaction
(c) Decomposition reaction
(d) Displacement reaction

Solution: (d)
Aluminum is more reactive than iron and displaces it from its oxide.

Section B: Assertion and Reason Questions

11. Assertion (A): Respiration is considered an exothermic reaction.

Solution: (a)
Energy is released during the breakdown of glucose.

Section C: Case Study Based Questions

16. In which test tube will a brown coating be observed on the iron nail?

Solution:
Test tube II (CuSO₄).

17. Why does no reaction occur in the test tube containing ZnSO₄?

Solution:
Iron is less reactive than zinc.

Section D: Short Answer Questions (2-3 Marks)

21. Why are decomposition reactions called the opposite of combination reactions?

Solution:
In a combination reaction, two or more substances combine to form a single product. In a decomposition reaction, a single reactant breaks down into two or more simpler products.

Section E: Long Answer Questions (5 Marks)

36. Explain the various types of chemical reactions with one balanced equation for each.

Combination:

C + O₂ → CO₂

Decomposition:

2FeSO₄ → Fe₂O₃ + SO₂ + SO₃

Displacement:

Zn + CuSO₄ → ZnSO₄ + Cu

Double Displacement:

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Part II: Competitive Level (NTSE, Olympiad, HOTS)

41. [HOTS] When lead nitrate powder is heated in a boiling tube, brown fumes are evolved.

Solution:
The brown fumes are Nitrogen dioxide (NO₂).

43. [Olympiad] In the reaction xKClO₃ → yKCl + zO₂, the values of x, y, z are:

(a) 2, 2, 3
(b) 1, 1, 1
(c) 3, 3, 2
(d) 2, 1, 3

Solution: (a)

2KClO₃ → 2KCl + 3O₂