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

Explanation

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