Answer:
The physical process responsible for the change in size of naphthalene balls is called sublimation. Sublimation is the phase transition where a substance changes directly from a solid to a gas without passing through the liquid state. In the case of naphthalene balls, over time, they can undergo sublimation, gradually changing from solid to vapor without melting into a liquid. This is why naphthalene balls can slowly decrease in size when exposed to air.