Give a reason for the following observations: (a) Naphthalene balls disappear with time without leaving any solid. (b) We can get the smell of perfumes sitting several metres away.

Reason for the following observations:
Naphthalene undergoes sublimation easily, that is the change of state of naphthalene from solid to gas without the intervention of the liquid state.
Thus, naphthalene balls keep forming naphthalene vapours that disappear into the air with time without leaving any solid.
Perfume has a higher degree of vaporization and the vapour diffuses into the air easily. Gaseous particles possess high speed with move very rapidly in all directions.
When perfume is sprayed, its particles diffuse into the air particles at a high-speed rate and reach our nostrils. This enables us to smell the perfume from a distance.
Final Answer:
Naphthalene undergoes sublimation easily, that is the change of state of naphthalene from solid to gas without the intervention of the liquid state.
Thus, naphthalene balls keep forming naphthalene vapours that disappear into the air with time without leaving any solid.
Perfume has a higher degree of vaporization and the vapour diffuses into the air easily. Gaseous particles possess high speed with move very rapidly in all directions.
When perfume is sprayed, its particles diffuse into the air particles at a high-speed rate and reach our nostrils. This enables us to smell the perfume from a distance.