True, air contains oxygen and oxygen is a supporter of combustion.
Air or oxygen which helps in burning is called supporter of combustion and the chemical reaction which takes place with the release of heat and light energy is called combustion.
A chemical process in which a substance reacts with oxygen to give off heat is called combustion. The substances which undergo combustion are known as combustible substances. It may also be called a fuel. Sometimes, heat is accompanied by light, either as a flame or as a glow, during combustion. Fuel may be solid, liquid or gas. A combustion reaction maybe written as-
(a) Charcoal burns in air to give carbon dioxide and heat.
C + O2 → CO2 + Heat