For `M^(2+) //M` and `M^(3+) //M^(2+)` system, `E^(@)` values for some metals are as follows `,`
`Cr^(2) //Cr= - 0.9 V l, Cr^(3+) //Cr^(2) = - 0.4 V, Mn^(2+) //Mn = - 1.2 V, Mn^(3+) //Mn^(2+) = + 1.5 V, Fe^(2+) //e= - 0.4 V, Fe^(3+) //Fe^(2+) = + 0.8 V`
Use this data to comment upon
(i) the stability of `Fe^(3+)` in acid solution as compared to that of `Cr^(3+)` and `Mn^(3+)`
(ii) the case with which iron can be oxidized as compared to the similar process for either Cr or Mn metals.

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^(@)` value. Hence, `Mn^(3+)` can be easily reduced to `Mn^(2+)` , i.e., `Mn^(3+)` is least stable. `E^(@)` value for`Fe^(3+)//Fe^(2+)` is positive but small. Hence, `Fe^(3+) ` si more stable than `Mn^(3+)` but less stable than `Cr^(3+)`
(ii) Oxidation potentials for the given pairs will be `+ 0.9 V , + 1.2 V` and `+ 0.4 ` volt . Thus, the order of their getting oxidized will be in the order `Mn gt Cr gt Fe`