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

(a) Naphthalene balls disappear with time without leaving any solid residue because of a process called sublimation. Naphthalene, the main component of naphthalene balls, has a relatively low melting point and readily sublimes from a solid to a gas without passing through the liquid phase. This means that over time, the naphthalene molecules on the surface of the balls transition directly from a solid to a gaseous state, leading to the disappearance of the balls without leaving behind any solid residue.

(b) We can get the smell of perfumes sitting several miles away due to the phenomenon of diffusion. Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. Perfume molecules evaporate from the surface of the perfume and diffuse through the air. Over time, these molecules spread out and mix with the surrounding air, traveling through the atmosphere even over long distances. This allows us to perceive the smell of perfumes from far away locations, provided that there are no significant barriers or obstacles blocking the diffusion of the perfume molecules.