Give reason for the following observations:

(a) Naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume sitting several metres away.

(a) Naphthalene balls when left open, directly change into vapour without heating due to sublimation. Hence, with time they become small in size and finally disappear.

(b) Perfumes comprise substances that are volatile, and diffuse rapidly into the air. Hence, we are able to smell perfume sitting several metres away.