How would you account for the following?
(i) `Cr^(2+)` is reducing in nature while with the same d-orbital configuration `(d^14) Mn^(3+)` is an oxidising agent.
(ii) In a transition series of metals, the metal which exhibits the greatest number of oxidation states occurs in the middle of the series.
(iii) Metal-metal bonding is more frequent for the 4d and the 5d series of transition metals than for the 3d series.