Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?
Maganese (Z = 25) shows maximum number of oxidation states. This is because its electronic configuration is 3d5 4s2. As 3d and 4s are close in energy, it has maximum number of electrons to lose or share (as all the 3d electrons are unpaired). Hence, it shows oxidation states from +2 to +7 (+2, +3, +4, +5, +6 and +7) which is the maximum number.