Question

Which of the following change cannot be reversed?
(a) Blowing of a balloon
(b) Folding a paper to make a toy aeroplane.
(c) Rolling a ball of dough to make roti
(d) Baking cake in an oven
(e) Drying a wet cloth
(f) Making biogas from cow dung.
(g) Burning of a candle.

Answer 1

(a)

Blowing of a balloon can be reversed because the balloon filled with air during blowing and when the air is released from the balloon it attains its original state. Hence, the given change is reversible.

(b)

Folding a paper to make a toy aeroplane can be reversed by unfolding the paper aeroplane to get back its original state.
Hence, the given change is reversible.

(c)

Rolling of chapati can be reversed because only the shape of the dough changes.
Hence, the given change is reversible.

(d)

Baking cake in an oven cannot be reversed because the cake batter gets cooked in the process.
Hence, the given change is irreversible.

(e)

Drying a wet cloth happens through evaporation of water and this process can be reversed through soaking the cloth back in water.
Hence, the given change is reversible.

(f)

Biogas production from decomposition of cow dung is irreversible.
Hence, the given change is irreversible.

(g)

When a candle burns, the wick burns and is converted to fumes, so the candle fire extinguishes after some time due to decrease in size of the wick.
Hence, the given change is irreversible.