Explanation:
A balanced chemical equation is defined as the one that contains same number of atoms on both reactant and product side.
Whereas a chemical reaction that brings change in oxidation state of the reacting species is known as a redox reaction.
When there occurs decrease in oxidation number of an element then it shows the element has been reduced. And, if there occurs an increase in oxidation state of an element then it means the element has been oxidized.
(a) The reaction between nitrogen and hydrogen to form ammonia will be as follows.
So here, oxidation state of nitrogen is changing from 0 to -3. Whereas oxidation state of hydrogen is changing from 0 to +3.
Reaction between ammonia and nitric acid will be as follows.
Since, it is a combination reaction. Therefore, no change in oxidation state of reacting species is taking place.
(b) Reaction for conversion of liquid bromine to hydrogen bromide is as follows.
Here, oxidation state of hydrogen is changing from 0 to +1. Therefore, oxidation of hydrogen is taking place. On the other hand, oxidation state of bromine is changing from zero to -1. Therefore, reduction of bromine is taking place.
(c) Reaction between Zn and S will be as follows.
Here, oxidation state of zinc is changing from 0 to +2. Hence, oxidation of zinc is taking place.
Oxidation state of sulfur is changing from 0 to -2. Therefore, reduction of sulfur is taking place.
