Oxidation and Reduction in terms of O.N are defined as given below:

1. Oxidation: A reaction in which oxidation number of the element increases.

2. Reduction: A reaction in which oxidation number of the elemnt decreases.

3. Oxidising agent (oxidant): A substance in which the oxidation number of atom increases.

4. Reducing agent (reductant) A substance in which oxidation number of atom decreases.