Question

what is the combustible and non combustible

Answer 1

the substances which can burn in air (in presence of oxygen) are called combustible whereas which cannot burn in presence of oxygen are called non combustible substances

Answer 2

Combustible substances are the substance that can catch fire easily. Another definition can be, The substances that have low ignition temperature are combustible.

Examples :-
Wood, Paper etc.

Non combustible substances are substances that do not catch fire easily. There ignition temperature is very high, that is, they are reverse of combustible substances.

Examples :-
Iron, steel etc