How would you account for the following. (i). Of the d^4 species. Cr^(2+) is strongly reducing while manganese (III) is strongly oxidising. (ii). Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised. (iii). The d^1 configuration is very unstable in ions.

How would you account for the following. (i). Of the d^4 species. Cr^

1.	How would you account for the following. (i). Of the d^4 species. Cr^(2+) is strongly reducing while manganese (III) is strongly oxidising. (ii). Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised. (iii). The d^1 configuration is very unstable in ions.
Answer» Solution :(i). `E^(ɵ)` value for `((Cr^(3+))/(Cr^(2+)))` is negative `(-0.41V)` whereas `E^(ɵ)` value for `((Mn^(3+))/(Mn^(2+)))` is positive `(+1.57V)`. Hence `Cr^(2+)` ions can easily undergo oxidation to GIVE `Cr^(3+)` ions and THEREFORE, act as STRONG reducing agent whereas `Mn^(2+)` can easilyundergo reduction to give `Mn^(2+)` and hence act as oxidising agent. (ii). `Co^(3+)` has greater tendecny to form coordination complexes than `Co^(2+)`. Hence in the presence of ligands `Co^(2+)` changes to `Co^(3+)` i.e., is easily oxidised. (iii) The ions with `d^1` configuration have the tendency to lose the only ELECTRON present in d-subshell to acquire stable `d^0` configuration. Hence, they are UNSTABLE and undergo oxidation or disproportionation.