Mothballs are made of naphtalene. The chemical structure of naphthalene is formed by two benzene rings, which gives this substance the classification of an aromatic compound.
The active principle of naphthalene is explained by a very interesting physical characteristic: sublimation, which is defined as the direct transition from a solid to a gaseous state. Once sublimated, naphthalene appears as a toxic vapor for undesirable microorganisms.
So, when a bag of mothballs is opened, they will sublime. So the molecules will not be able to come back to the bag, because they're in the gaseous state, which is too difficult for us to "pick up" the molecules of mothballs again and place them in their bag again.
It is like picking up water vapor, it is impossible.
Answer: Alternative "D"