Question

Define the following Sublimation

Answer 1

A change of state directly from solid to gas without changing into liquid state is called sublimation. For example, when ammonium chloride is heated, it changes directly from the solid state into the gaseous state. Similarly naphthalene balls, dry ice also undergo sublimation. 
or

 Sublimation can be defined as the  change of solid state of a substance directly to gaseous state without  changing to liquid state and vice-versa. some substances that are sublime are-

                  naphthalene, carbon dioxide,anthracene etc.

Answer 2

The process in which the change of solid state into gaseous state on increase in temperature without undergoing liquid state . And by decreasing the temperature the substance again turns into solid state without turning into liquid state.Example :- Napthalene , Camphor etc.
one important point that only sublime substance undergoes sublimation.
Hope this helps you.☺☺☺