# The standard reduction potentials at 298K for following half reaction are given against each.$Zn^{+2}(aq)+2e^-\leftrightharpoons 2n(s)=-0.762$ $Cr^{+3}(aq)+3e^-\leftrightharpoons Cr(s)=-0.740$ $2H^+(aq)+3e^-\leftrightharpoons H_2(g)=0$ $Fe^{+3}(aq)+e^-\leftrightharpoons Fe^{+2}(aq)=0.770$. Which is the strongest reducing agent ?

$\begin{array}{1 1}(a)\;Zn(s)\\(b)\;Cr(s)\\(c)\;H_2(g)\\(d)\;Fe^{+2}(aq)\end{array}$

$Zn^{+2}(aq)$ having minimum reduction potential.So oxidation potential of Zn(s) will be maximum and it will be strongest reacting agent.
Hence (a) is the correct answer.