Question

Which metal exhibits more than one oxidation state in its compounds?

• A. $Na$
• B. $Mg$
• C. $Al$
• D. $Fe$

Answer 1

The correct option is D $Fe$

Transition elements show variable oxidation state because their valence electrons in two different sets of orbitals, that is (n-1)d and ns. The energy difference between these orbitals is very less, so both the energy levels can be used for bond formation. Thus, transition elements have variable oxidation states.
Since iron $\left(Fe\right)$ is a transition metal, it shows variable oxidation states.