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

<p>The element among the given options that shows only one oxidation state other than its elemental form is <strong>Scandium</strong>.</p> <p>Explanation:</p> <ul> <li><strong>Nickel (Ni)</strong> can have multiple oxidation states, including +2 and +3, with +2 being the most common.</li> <li><strong>Titanium (Ti)</strong> also shows various oxidation states, most commonly +4 and +2, due to its ability to lose electrons from both its 3d and 4s subshells.</li> <li><strong>Cobalt (Co)</strong> commonly exists in the +2 and +3 oxidation states, among others, due to electron transitions in its 3d orbitals.</li> <li><strong>Scandium (Sc)</strong>, however, primarily exhibits a +3 oxidation state in its compounds (excluding its 0 state in the elemental form). This is because scandium has an electronic configuration of [Ar]3d¹4s², and it loses all three outer electrons to achieve a stable configuration, resulting in a +3 oxidation state. It does not commonly exhibit other oxidation states because removing more than three electrons would require removing electrons from the very stable noble gas core configuration ([Ar]), which is energetically unfavorable.</li> </ul> <p>Therefore, the correct answer is <strong>Option D: Scandium</strong>.</p>