At 298 K the standard reduction potentials for the following half reactions are given as 
$\begin{array}{l}{{\mathrm{Zn}}^{2+}}_{\left(\mathrm{aq}\right)}+2{\mathrm{e}}^{-}⟶{\mathrm{Zn}}_{\left(\mathrm{s}\right)};-0.762\mathrm{V}\\ {{\mathrm{Cr}}^{3+}}_{\text{(aq) }}+3{\mathrm{e}}^{-}⟶{\mathrm{Cr}}_{\left(\mathrm{s}\right)};-0.740\mathrm{V}\\ 2{{\mathrm{H}}^{+}}_{\text{(aq) }}+2{\mathrm{e}}^{-}⟶{\mathrm{H}}_{2(\mathrm{g}};-0.00\mathrm{V}\\ {{\mathrm{Fe}}^{3+}}_{\text{(aq) }}+{\mathrm{e}}^{-}⟶{\mathrm{Fe}}^{2+}\text{ (aq) };+0.770\mathrm{V}\end{array}$
The strongest reducing agent is