Give reasons for the following observations:

(a) Naphthalene is a volatile organic compound which can undergo sublimation. It directly changes into vapour state without leaving any solid. The naphthalene balls sublime completely forming naphthalene vapours and hence, they disappear without leaving any solid residue.

(b) Perfume contains a volatile solvent which diffuses into the air. When liquid perfume is applied, it quickly changes into vapours. As a result of diffusion, the perfume vapours move very rapidly in all directions in air, mix up with air particles and spread in the air. When this air containing perfume vapours reaches several metres away, we can smell the perfume.