How would you account for the following:
A) Of the `d^(4)` species `Cr^(2+)` is strongly reducing while manganese(III) is strongly oxidizing.
B) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidized.
C) The `D^(1)` configuration is very unstable in ions.

Explanation

`E^(@)` value of `Cr^(3+)//Cr^(2+)` is negative (-0.41 V) while that of `Mn^(3+)//Mn^(2+)` is positive (+1.57 V). This means `Cr^(2+)` ions can lose electrons to form `Cr^(3+)` ions and act as a reducing agent while `Mn^(3+)` ions can accept electrons and can act as oxidising agent..
(b) Cobalt(II) is stable in aqueous solution but in the presence of complexing agent, it undergoes change in oxidation state from +2 to +3 and is easily oxidised.
(c) Tha ion with `d^(1)` configuration is expected to be extremely unstable and has a great urge to acquire `d^(@)` configuration ( very stable) by losing the only electron present in the d-sub-shell.