The standard reduction potentials of $2 \mathrm{H}^{+} / \mathrm{H}_2, \mathrm{Cu}^{2+} / \mathrm{Cu}$.…
The standard reduction potentials of $2 \mathrm{H}^{+} / \mathrm{H}_2, \mathrm{Cu}^{2+} / \mathrm{Cu}$. $\mathrm{Zn}^{2+} / \mathrm{Zn}$ and $\mathrm{NO}_3{ }^{-}, \mathrm{H}^{+} / \mathrm{NO}$ are $0.0,-0.34,-0.76$ and 0.97 V respectively. Observe the following reactions
I. $\mathrm{Zn}+\mathrm{HCl} \rightarrow$
II. $\mathrm{Cu}+\mathrm{HCl} \rightarrow$
III. $\mathrm{Cu}+\mathrm{HNO}_3 \rightarrow$ Which reactions does not liberate $\mathrm{H}_2(\mathrm{~g})$ ?
II, III only
I, II only
I, III only
I. II, III
Solution
Higher the reduction potential less in the tendency to librate $\mathrm{H}_2$ gas.