Question

B. Tick () the correct choice.
1. Which of the following is a periodic change?
(a) blowing of wind
(b) growth of animals
(c) rotation of the earth
(d) evaporation of water
2. Which of the following is not a physical change?
(a) breaking of a brick
(b) evaporation of a liquid
(c) burning of a candle
(d) moving of a wheel
3. physical changes are
(a) always irreversible
(b) always reversible
(c) mostly irreversible
(d) mostly reversible
4. A substance which increases the rate of a reaction and remains unchanged is called,
(a) reactant
(b) product
(c) catalyst
(d) none of these​

Answer 1

Answer:

Below is the answer...

Explanation:

1.Rotation of earth

2. Burning of a candle

3 .Mostly irreversible

4.Catalyst

Answer 2

1. The correct answer is option (c) Rotation of the earth.

Explanation: Rotation of earth happens during a period of time i.e. 24 hrs. therefore, rotation of earth is a periodic change.

2. The correct answer is option (c) Burning of a candle.

Explanation: When a candle burns, the oxygen in the air reacts and forms carbon dioxide. A new substance, the CO2 is formed, So it is a chemical change.

3. The correct answer is option (d) mostly reversible.

Explanation: Physical changes are mostly reversible because they involve changes in the physical properties of a substance such as state, shape, size, colour etc. and no new substances are formed in a physical change.

4. The correct answer is option (c) Catalyst

Explanation: Any substance that increases the rate of a reaction without itself being consumed is known as catalyst.