A solution containing 1 M each of ${\mathrm{Cu}}^{2+},{\mathrm{Ag}}^{+},{\mathrm{Mg}}^{2+}$ and ${\mathrm{Hg}}^{2+}$ is electrolysed using inert electrodes. If $E^{\circ }\left({\mathrm{Ag}}^{+}\mid \mathrm{Ag}\right),E^{\circ }\left({\mathrm{Hg}}^{2+}\mid \mathrm{Hg}\right),E^{\circ }\left({\mathrm{Cu}}^{2+}\mid \mathrm{Cu}\right)$ and $E^{\circ }\left({\mathrm{Mg}}^{2+}\mid \mathrm{Mg}\right)$ are$0.80 \mathrm{V}, 0.79 \mathrm{V}, 0.34 \mathrm{V}$ and $-2.37 \mathrm{V}$, respectively, the sequence of deposition of metals on the cathode with the increasing potential is

The propensity for deposition increases with decrease potential.

Ag has a negative reduction potential, therefore it has no inclination to deposit and cannot be produced by electrolyzing aqueous salt solutions. Reduction potential order is Ag> Hg> Cu, so they decompose in that order.

Hence option C is correct