The E^° value for the Mn^3+ / Mn^2+ couple is more positive than that of Cr^3+ / Cr^2+ or Fe^3+ / Fe^2+ due to change of

The $\displaystyle \mathrm{E}^{\circ}$ value for the $\displaystyle \mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ couple is more positive than that of $\displaystyle \mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}$ or $\displaystyle \mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}$ due to change of