Question

explain how camphor disappers without leaving any residue

Answer 1

Camphor is 1 of the substances which directly turns to gaseous state (skipping liquid state) by gaining kinetic energy.
Therefore it evaporates without leaving any residue.
The process of conversion of a substance from solid directly to liquid is called Sublimation.

Answer 2

Camphor disappears after some time as its surface gains kinetic energy and directly gets converted into gas. The process of converting directly into gaseous form and not in a liquid state is termed as sublimation. Hence, when camphor is given fire, it gets converted into gas and disappears, without leaving any residue.