The standard potentials at 298 K are

$E^{\circ }\left({\mathrm{Zn}}^{2+}\mid \mathrm{Zn}\right)=-0.763\mathrm{V},E^{\circ }\left({\mathrm{Cr}}^{3+}\mid \mathrm{Cr}\right)=-0.41\mathrm{V}$

$E^{\circ }\left({\mathrm{H}}^{+}\left|{\mathrm{H}}_2\right|\mathrm{Pt}\right)=0.00$   and  $E^{\circ }\left({\mathrm{Fe}}^{3+},{\mathrm{Fe}}^{2+}\mid \mathrm{Pt}\right)=0.770\mathrm{V}$

Which is the strongest reducing agent?

Solution:

The smaller the value of reduction potential, lesser the reduction tendency of the ion and larger the oxidation tendency of the corresponding metal. Larger oxidation tendency implies stronger reducing agent.

A reducing agent is a substance that undergoes oxidation to a higher valency state in a redox reaction and loses electrons to other substances in the process. In an oxidation-reduction process, a reducing agent is one of the reactants that reduces another reactant by discharging electrons onto it.