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

We need to identify which element shows only one oxidation state other than its elemental form (0).

Cobalt (Co, Z = 27): Shows +2 and +3 oxidation states. Multiple oxidation states.

Titanium (Ti, Z = 22): Shows +2, +3, and +4 oxidation states. Multiple oxidation states.

Nickel (Ni, Z = 28): Shows +2 and +3 oxidation states. Multiple oxidation states.

Scandium (Sc, Z = 21): Electronic configuration is $$[Ar]3d^1 4s^2$$. It has only 3 electrons beyond the noble gas core. When these 3 electrons are removed, it achieves the very stable noble gas configuration of Argon. Therefore, Sc shows only the +3 oxidation state. The +1 and +2 states are not observed because partial removal of electrons does not give any special stability.

The correct answer is Option (4): Scandium.