Question

Which of the following are chemical changes:

(i) Cutting of trees

(ii) Burning of paper

(iii) Boiling of water to form steam

(iv) Rusting of iron almirah

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

Answer 1

The correct option is C

(ii) and (iv)

1. Physical changes are those in which the physical properties of the substances change. It is reversible and no new product is formed. Example: Conversion of water into steam.
2. Chemical changes are irreversible and a new product is formed. Example: Digestion of food.

The explanation for the correct option:

(c) burning of paper and rusting of iron almirah:

1. The burning of paper is a chemical change as ash and gases are produced as a by-product of the combustion of paper.
2. We can't get back the piece of paper burned.
3. Rusting of iron almirah is a chemical change that occurs when two chemicals react to form a new material.
4. When iron gets oxidised it forms an iron oxide that is reddish-brown in colour known as rust.

The explanation for incorrect options:

Cutting of paper:

No new substance is formed only the shape of the matter has changed thus it's a physical change.

Boiling of water to form steam:

No new substance is formed only the state of water changes from liquid (water) to gaseous vapours (steam) thus it's a physical change.

Since cutting of paper and boiling of water to form steam are physical changes thus options (a), (b) and (d) are incorrect.

Hence, option (c) is the correct option.