In a transition series of metals the metal which exhibits the greatest no. Of oxidation states occurs in the middle of the series

In a transition series, the filling of d orbitals takes place. First all the five d-orbitals are singly filled and then pairing starts. The middle member of the series has singly filled d orbitals and thus the maximum number of unpaired electrons. So, the greatest number of oxidation states is shown by the element present in the middle of a series. For example: In first series, manganese show maximum number of oxidation states ( +2 to +7).