The element which shows only one oxidation state other than its elemental form is :

Solution

Chemistry ma’am · 3 steps

Scandium gives away all three outer electrons together, lands on the argon core and stops there.

1. Why states vary. In transition metals the 3d and 4s electrons have very similar energies. So these atoms can lose different numbers of electrons, which gives several oxidation states.

   Element	Configuration	Common oxidation states
   Sc	[Ar] 3d¹ 4s²	+3 only
   Ti	[Ar] 3d² 4s²	+2, +3, +4
   Co	[Ar] 3d⁷ 4s²	+2, +3
   Ni	[Ar] 3d⁸ 4s²	+2 (also +3, +4 in some compounds)

2. Scandium stops at +3. Scandium has only three electrons beyond argon. When it loses all three, Sc³⁺ has the stable noble gas configuration [Ar]. Keeping one 3d electron gives no extra stability, so +2 and +1 are not seen in its ordinary compounds.
3. So. Scandium shows only one oxidation state, +3, so the answer is (d).

The idea to keep. The ends of the 3d series show fewer oxidation states: Sc has too few d electrons to lose and Zn has too many to give up. Sc is only +3 and Zn is only +2.

Answer from the NTA final answer key. Solution by PrepWiser.