Q. The standard reduction potentials at 298 K for the following half-cell reactions are given ${Zn}^{2 +}\ (aq)\ + \ {2e}^{-}\ \ \rightleftharpoons \ \ Zn\ (s);\ \ \ \ \ \ \ \ - 0.762\ V$ ${Cr}^{3 +}\ (aq)\ + \ {3e}^{-}\ \ \rightleftharpoons \ \ Cr\ (s);\ \ \ \ \ \ \ \ - 0.74\ V$ ${2H}^{+}\ (aq) + \ {2e}^{-}\ \ \rightleftharpoons \ H_{2}(g);\ \ \ \ \ \ \ \ \ \ + 0.00\ V$ ${Fe}^{3 +}\ (aq) + \ e^{-}\ \ \rightleftharpoons \ {Fe}^{2 +}\ (aq);\ \ \ + 0.77\ V$ Which one of the following is the strongest reducing agent?
A) Zn (s)
B) Cr(s)
C) $H_{2}$ (s)
D) ${Fe}^{2 +}$ (aq)
Explanation
(a)
The metals having higher negative value of standard reduction potential are placed above hydrogen in electrochemical series. The metals places above hydrogen has a great tendency to donate electrons or oxidising power. The metals having great oxidizing power are strongest reducing agent. Zn has higher negative value of standard reduction potential. Therefore, it is the strongest reducing agent.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.