Why is the `E^(ϴ)` value for the `Mn^(3+)//Mn^(2+)` couple much more positive than that for `Cr^(3+)//Cr^(2+)" or "Fe^(3+)//Fe^(2+)` ? Exaplain.

Answer

Much larger third ionisation energy of `Mn` (where the required is `d^(5) to `D^(4)` ) is mainly responsible for this . This also explain why the `+3` state of `Mn`is of little importance.