# 8.17 For $M^{2+}/M$and $M^{3+}/M^{2+}$ systems the $E^{\ominus }$ values for some metals are as follows:         $\\Cr^{2+}/Cr\; \; \; \; \; \; \; \; \; \; \; \; -0.9V\\Mn^{2+}/Mn\; \; \; \; \; \; \; \;\; \; -1.2V\\Fe^{2+}/Fe\; \; \; \; \; \; \; \; \; \; \; \; \; -0.4V$          $\\Cr^{3}/Cr^{2+}\; \; \; \; \; \; \; \; \; \; \; \; -0.4V\\Mn^{3+}/Mn^{2+}\; \; \; \; \; \; \; \; +1.5V\\Fe^{3+}/Fe^{2+}\; \; \; \; \; \; \; \; \; \; \; +0.8V$         Use this data to comment upon:(ii) the ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.

From the values of $\dpi{100} E^{o}$, the order of oxidation of the given metal to the divalent cation is-
$\dpi{100} Mn>Cr>Fe$