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.

(N/A) Naphthalene is a substance that undergoes sublimation,meaning it changes directly from a solid to a gas without passing through the liquid state. As it absorbs heat from the surroundings,the naphthalene balls sublime and disappear over time.
$(b)$ The smell of perfume is due to the presence of volatile aromatic compounds. These particles diffuse rapidly through the air,allowing us to detect the scent even when sitting several metres away.