The standard potentials $\left(\mathrm{E}°\right)$ of ${\mathrm{MnO}}_4^{-}/{\mathrm{Mn}}^{2+}$ ${\mathrm{MnO}}_2/{\mathrm{Mn}}^{2+}$ half cells in acidic medium are $1.51 \mathrm{V}$ and $1.23 \mathrm{V}$ respectively at $298 \mathrm{K}$. The standard potential of ${\mathrm{MnO}}_4^{-}/{\mathrm{MnO}}_2$ half-cell in acidic medium at the same temperature is:

When a metal is electroplated with silver $\left(\mathrm{Ag}\right)$ 

$\mathrm{E}$ of the given cell is:

$\mathrm{Ni}\left|({\mathrm{Ni}}^{+2},1.0\mathrm{M})\Vert \left({\mathrm{Co}}^{+2},1.0\mathrm{M}\right)\right|\mathrm{Co}$

From the given standard electrode potentials,
${\mathrm{Sn}}^{4+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to {\mathrm{Sn}}^{2+}\left(\mathrm{aq}\right) \mathrm{E}°=0.15 \mathrm{V}$

${\mathrm{Br}}_2\left(\mathrm{l}\right)+2{\mathrm{e}}^{-}\to 2{\mathrm{Br}}^{-}\left(\mathrm{aq}\right) \mathrm{E}°=1.07 \mathrm{V}$

The approximate free energy change of the process $2{\mathrm{Br}}^{-}\left(\mathrm{aq}\right)+{\mathrm{Sn}}^{4+}\left(\mathrm{aq}\right)\to {\mathrm{Br}}_2\left(\mathrm{l}\right)+{\mathrm{Sn}}^{2+}\left(\mathrm{aq}\right)$ is