Why do transition elements show variable oxidation states ? In 3d series (Sc to Zn), which element shows the maximum number of oxidation states and why ?

Explanation

Transition elements show variable oxidation states because the energies of (n − 1)d and ns are similar. Electrons from both may take part in bonding giving variable oxidation states.
Manganese shows the maximum number of oxidation states. It has the electronic configuration `3d^(5)4s^(2)`. On sharing 2 electrons of 4s and successive sharing of 5 electrons of 3d orbital, it gives oxidation states of +2, +3, +4, +5, +6 and +7.