Naphthalene balls become smaller in size when kept exposed for a few days. This is because of sublimation.
Have you ever seen napthalene balls? They are not very popular these days but they used to be in the 1990s. They kind of look like mentos. They were used to keep clothes smelling better and to prevent damange from moths and fungus.
But how can some solid balls do that? It's because they convert to a gas directly and give out a kind of sweet, pungent smell. As they get converted more and more to a gas, they keep shrinking. And eventually, the balls disappear and you'll have to replace them.
This conversion from a solid to a gas directly is called sublimation.