Question

naphthalene balls disappear with time without leaving any solid why​

Answer 1

Naphthalene balls undergo sublimation and convert into the vapours directly and disappear into air without leaving any solid.

Answer 2

Naphthalene ball is a sublimable substance which undergoes sublimation i.e. conversion of solid state to gaseous state or gaseous state to solid state without undergoing the intermediate state of liquid. That's why, naphthalene balls disappear with time without leaving any solid.