The limited supply of air leads to incomplete combustion of fuel, which in turn leads to the production of black smoke.

Oxidation is the addition of oxygen to a substance or the removal of hydrogen from a substance. The reaction in which heat energy is produced is called exothermic reaction.

(i) Photosynthesis in plants (ii) Respiration in the human body (iii) Decomposition of vegetable matter (iv) Decomposition of ferrous sulphate.