Q. How to change in Oxidation Number in Redox Reactions?

Ans.

In reduction-oxidation, or redox, reactions, atoms undergo changes in their oxidation numbers.

Consider the following reaction:

2Na + Cl₂ -> 2Na+ + 2Cl^-

In this equation, the oxidation number of sodium increases from 0 to +1 and that of chlorine decreases from 0 to -1. Therefore, we can say that sodium is oxidized and chlorine is reduced.

Consider another reaction:

H₂(g) + Cl₂(g) -> 2HCl(g)

The reaction of hydrogen with chlorine, like that of sodium with chlorine, is an example of a redox reaction. In this equation, the oxidation number of hydrogen increases from 0 to +1, and that of chlorine decreases from 0 to -1. Hence hydrogen is considered to be oxidized, and chlorine is considered to reduced. Thus, this reaction is also a redox reaction.