Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?

Manganese (Z = 25) exhibits the largest number of oxidation states. This is because its electronic configuration is 3d⁵4s².

Because it has the maximum number of electrons (5 d electrons and 2s electrons) to easily lose and share.

Therefore, it can exhibit an oxidation state of +2 to +7.

The compounds are as follows:

Mn(0) as Mn(s), Mn(II) as MnO, Mn(II,III) , Mn etc.