How would you account for the following?
(a) Transition metals exhibit variable oxidation states.
(b) Zr(Z = 40) and Hf (Z = 72) have almost identical radii.

Explanation

ns and (n-1) d electrons of transition metals participate in bonding, which result in variable oxidation states. When ns electrons take part in bonding , they exhibit lower oxidation states, whereas when (n-1) d-electrons participate in bonding, they exhibit higher oxidation states .