It is a chemical process in which the substance burns in the presence of oxygen to give heat and light. The substance which burns in the presence of oxygen is called a fuel.

Examples- Coal burns in air to give carbon dioxide, heat and light.

·          Carbon burns to give Carbon dioxide, heat and light.

C + O₂ = CO₂ + heat + light

·          Methane or Marsh gas burns to give Carbon dioxide, water vapors, heat and light

CH₄ + 2O₂ = CO₂ + 2H₂O + heat + light