The exhibition of various oxidation states by an element is also related to the outer orbital electronic configuration of its atom. Atom (s) having which of the following outermost electronic configurations will exhibit more than one oxidation state in its compounds.

1.   3s1

2.  3d14s2

3.  3d24s2

4.  3s23p3

(b, c, d)
Elements which have only s-electrons in the valence shell do not show more than one oxidation state. Thus, element with 3s1 as outer electronic configuration shows only one oxidation state of +1.
Transition element such as elements (b), (c) having incompletely filled d-orbitals in the penultimate shell show variable oxidation states. Thus, element with outer electronic configuration as 3d14s2 shows variable oxidation states of +2 and +3 and the element with outer electronic configuration as 3d24s2 shows varibale oxidation states of +3 and +5 due to involvement of d-orbitals.