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.

Answer:

• Sublimation, or the change of state of naphthalene from solid to gas without the intervention of the liquid state, is a simple process. As a result, naphthalene balls continue to create naphthalene vapours, which dissipate into the air over time without leaving any solid residue.
• Perfume has a higher vaporisation rate, and its vapour easily diffuses into the air. Gaseous particles have a high velocity and move quickly in all directions. When perfume is applied, its particles quickly drift into the air and reach our nostrils. As a result, we can smell the perfume from a far.