Passage :

            A reaction in which oxidation and reduction takes place simultaneously is called redox reaction.

Example: ${\stackrel{0}{\text{Zn}}}_{\text{(s)}}+\stackrel{+2}{\text{Cu}}{\text{SO}}_{\text{4(aq)}}\to \stackrel{+2}{\text{Zn}}{\text{SO}}_{\text{4(aq)}}+{\stackrel{0}{\text{Cu}}}_{\text{(s)}}$

                  Zn is oxidized and acts as reducing agent.

                              Cu is reduced and acts as oxidizing agent.

Q.   In ${\text{Cr + Pb(NO}}_3{)}_2\to \text{Cr}{\left({\text{NO}}_{\text{3}}\right)}_3+\text{Pb}$,  reducing agent is