Assign reasons for each of the following `:`
(i) Manganese exhibits the highest oxidation state of `+7` .
(ii) Unlike `Cr^(3+), Mn^(2+), Fe^93+)` and the subseuent `M^(3+) ` ions of 3d series of elements , the 4d an 5d series metals generally do not form stable cationic species.

Explanation

(i) Electronic configuration of `._(25)Mn` is `3d^(5) 4s^(2)` . As all the 7 electrons of 3d and 4s can participate in bonding , it exhibits highest oxidation state of `+7`
(ii) In the 4d and 5d series higher oxidation states are more stable ( because difference of energy between 4d and 5s or 5d and 6s is smaller than between 3d and 4s). In the higher oxidation states, bonds formed are mostly covalent .Hence they do not form cationic species.