`Co^(2+)` is easily oxidised to `Co^(3+)` in the presence of a strong ligand. Explain.

Explanation

In presence of weak ligand, `Co^(2+)` `(d^(7))` has electronic configuration `t_(2)^(5)e_(g)^(2)` i.e., there are three unpaired electrons. But in presence of a strong ligand, difference in energy between `t_(2g)` and `e_(g)` levels increases. So, out of three unpaired electrons two becomes paired and there remains only one unpaired electron in `e_(g)` level. This electron from higher energy `e_(g)` level is easily lost to form `Co^(3+)` ion having stable configuration `t_(2g)^(6)` with high CFSE. Thus `Co^(2+)` is easily oxidised to `Co^(3+)` in presence of strong ligand.