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

Explanation

(i). `((Cr^(3+))/(Cr^(2+)))` has a negative reduction potential. Hence, `Cr^(3+)` cannot be reduced to `Cr^(2+)`, i.e., `Cr^(3+)` is most stable. `((Mn^(3+))/(Mn^(2+)))` has large positive `E^(ɵ)` value for `((Fe^(3+))/(Fe^(2+)))` is positive but small. Hence, `Fe^(3+)` is more stable than `Mn^(3+)` but less stable than `Cr^(3+)`.
(ii). Oxidation potential for the given pairs will be `+0.9V,+1.2V` and `+0.4volt`. Thus, the order of their getting oxidised will be in the order `MngtCrgtFe`.