The `E^(@)` value in respect of the electrodes `(Z=24)`, manganese `(Z=25)` and iron `(Z=26)` are :

`Cr^(3+)//Cr^(2+)=-0.4V,Mn^(3+)//Mn^(2+)=+1.5V`,`Fe^(3+)//Fe^(2)=+0.8V`.

On the basic of the above information compare the feasibilities of further oxidation of their `+2` oxidation states.

Explanation

`-ve` value of `E^(@)` for `Cr^(3+) //Cr^(2+)` shows that `Cr^(2+)` is least stable. Greater `+ve` value for `Mn^(3+)// Mn^(2+)` than that for `Fe^(3+) //Fe^(2+)` shows that `Mn^(2+)` is more stable than `Fe^(2+)` . Hence, stability of `+2` oxidation state is in the order `: Cr^(2+) lt Fe^(2+) lt Mn^(2+)` or the oxidation of their `+2` state to `+3` state is in the order `: Cr^(2+) gt Fe^(2+) gt Mn^(2+)`