How would you account for the following :
Of the `d^(4)` species, `Cr^(2+)` is strongly reducing while manganese (III) is strongly oxidising.

Explanation

Standard reduction potential `(E^(0))` values for `Cr^(3+)|Cr^(2+)` and `Mn^(3+)|Mn^(2+)` couples are -
`Cr^(3+)(aq)+e rarr Cr^(2+)(aq), E^(0)=-0.41V`
`Mn^(3+)(aq)+e rarr Mn^(2+)(aq), E^(0)=+1.57 V`
`E^(0)` values indicate that `Cr^(2+)` ion can undergo ready oxidation to `Cr^(3+)` ion and hence, `Cr^(2+)` ion acts as reducing agent, whereas `Mn^(3+)` ion can undergo ready reduction to `Mn^(2+)` ion and therefore, acts as as oxidising agent. [Reductant of a couple with less `E^(0)` value is a good reducing agent, while oxidant of a couple with high `E^(0)` value is a good oxidising agent.]