JEE Main · 2021 · 24 Feb 2021 · Shift 1 · Redox Reactions and Electrochemistry

The standard electrode potential ($E^{\circ }$) for the $\mathrm{M}{}^{2+}/\mathrm{M}$ couple indicates the tendency of the metal ion to be reduced to the metal. A positive value means the metal ion is easily reduced (or the metal is less reactive).

For the 3d-series elements:

• $\mathrm{Zn}{}^{2+}/\mathrm{Zn}$: $E^{\circ }=-0.76$ V
• $\mathrm{Co}{}^{2+}/\mathrm{Co}$: $E^{\circ }=-0.28$ V
• $\mathrm{Fe}{}^{2+}/\mathrm{Fe}$: $E^{\circ }=-0.44$ V
• $\mathrm{Cu}{}^{2+}/\mathrm{Cu}$: $E^{\circ }=+0.34$ V

Only copper (Cu) shows a positive electrode potential value among the given options. This is because copper is less reactive and its ions are more easily reduced compared to the other metals listed.