How would you account for the following:
(i) `Cr^(2+)` is reducing in nature while with the same d-orbital configuration `(d^4) Mn^(3+)` is an oxidising agent.
  (ii) In a transition series of metals, the metal which exhibits the greatest number of oxidation state occurs in the middle of the series. 

Explanation

(i) `Cr^(2+)` is reduction as its configuration changes from `d^(5)` to `d^(3)`, the latter having half filled `t_(2g)` level whereas oxidation of Mn from `Mn^(2+)` to `Mn^(3+)` results in half filled do configuration, which is more stable.
(ii) In a transition metals series the oxidation state first increases and then decreases, At the middle it is maximum due to greater number of unpaired electron in (n-1)d and ns-orbitals.