Step-by-step explanation:
An equation that contains equal number of atoms on both reactant and product side is known as a balanced chemical equation.
Whereas when there will be increase in oxidation number of the atom then it is known as oxidation. When there is decrease in oxidation number of the atom then it is known as reduction.
For example,

Oxidation half reaction :

Reduction half reaction :

Therefore, we can conclude that sulfur atom has undergone oxidation and nitrogen atom has undergone reduction.