For `M^(2+)//M and M^(3+)//M^(2+)` systems the `E_0` values for some metals are as follows:
`{:(Cr^(2+)//Cr,-0.9 V, Cr^3//Cr^(2+),-0.4V),(Mn^(2+)//Mn, -1.2 V, Mn^(3+)//Mn, +1.5V),(Fe^(2+)//Fe, -0.4V. Fe^(3+)//Fe^(2+),+0.8V):}`
Use this data to comment upon :
(i) The stability of `Fe^(3+ )` in acid solution as compared to that of `Cr^(3+)` or `MnO^(3+)`, and
(ii) The case with which iron can be oxidised as compared to similar process for either chromium or manganese metal.

Explanation

(i) Higher the reduction potential of a species, greater is the tendency for its reduction to take place. Therefore, `Mn^(3+)` with highest reduction potential would be readily reduced to `Mn^(2+)` and hence is the least stable.
Thus, from the values of reduction potential, it is clear that stability of `Fe^(3+)` in acidic solution is more stable Mn + but less stable than that of `Cr^(3+)`.
(ii) Lower the reduction potential or higher the oxidation potential of a species, greater the ease with which its oxidation will take place. Thus, order of tendency to undergo oxidation is Fe < Cr Mn.