Unlike `Cr^(3+), Mn^(2+), Fe^(3+)` and the subsequent `M^(3+)` ions of 3d series of elements, the 4d and 5d series metals generally do not form stable cationic species. Explain.

Explanation

In the 4d and 5d series of elements, higher oxidation states are stable because difference of energy between 4d and 5d or between d and 6d is small. In the higher oxidation states, bonds formed are mostly covalent. Hence the metals of 4d and 5d-series do not form cationic species.