Explanation:
Reduction means the gain of electrons or decrease in number of oxidation state of an atom.
For example, [tex]H_{2}O + Cl_{2} + SO_{2} \rightarrow HCl + H_{2}SO_{4}[/tex]
Reduction half reaction: [tex]Cl_{2} + 1e^{-} \rightarrow Cl^{-1}[/tex]
Here oxidation state of chlorine changes from 0 to -1, that is, chlorine is reducing in this chemical reaction.