Give reasons 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 is a volatile organic compound which can undergo sublimation. It directly changes into vapor state without leaving any solid. The naphthalene balls sublimate completely forming naphthalene vapors 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 vapors. As a result of diffusion, the perfume vapors move very rapidly in all directions in air, mix up with air particles and spread in the air. When this air containing perfume vapors reaches several meters away, we can smell the perfume.