Question

The standard reduction potentials at $298K$ for the following half-cell reactions are given on next page
$\mathrm{Zn}{}^{2+}(\mathrm{aq})+2\mathrm{e}{}^{-}\rightleftharpoons \mathrm{Zn}(\mathrm{s})-$ $0.762$
$\mathrm{Cr}{}^{2+}(\mathrm{aq})+3\mathrm{e}{}^{-}\rightleftharpoons \mathrm{Cr}(\mathrm{s})-$ $0.74$
$2\mathrm{H}{}^{+}(\mathrm{aq})+2\mathrm{e}{}^{-}\rightleftharpoons \mathrm{H}{}_2(\mathrm{g})-$ $0.00$
$\mathrm{Fe}{}^{3+}(\mathrm{aq})+\mathrm{e}{}^{-}\rightleftharpoons \mathrm{Fe}{}^{2+}(\mathrm{aq})+$ $0.77$
Which one of the following is the strongest reducing agent ?

• A. $Zn(s)$
• B. $Cr(s)$
• C. $H_2(s)$
• D. $F{e}^{2+}(aq)$

Answer 1

Answer: (A)

The metals having higher negative value of standard reduction potential are placed above hydrogen in electrochemical series. The metals placed above hydrogen has a great tendency to donate electrons or oxidising power. The metals having great oxidising power are strongest reducing agent. Zn has higher negative value of standard reduction potential. Therefore, it is the strongest reducing agent.