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.

Answer

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