The standard potentials (E^ ^ ^ ) of MnO_4^ - / Mn^ 2+ and MnO_2 /...

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