Why do transition metals exhibit variable oxidation states?

Transition metals exhibit variable oxidation states because of the way their electrons are arranged. Here’s a explanation:

1. Electrons in d and s orbitals:
   • Transition metals have electrons in the (n-1)d and ns orbitals.
   • Both types of electrons can be lost during reactions, giving different positive charges.
2. Similar energy levels:
   • The energy difference between ns and (n-1)d electrons is small.
   • This makes it easy for the metal to lose different numbers of electrons, leading to multiple oxidation states.
3. Stability of oxidation states:
   • Some oxidation states are more stable due to half-filled or fully filled d-orbitals.
   • For example, +2 and +3 are common in iron, while +2 and +4 occur in manganese.

In short:
Transition metals show variable oxidation states because both d and s electrons can participate in bonding, and the small energy difference allows multiple possible states.