Cobalt (Co): Cobalt commonly exhibits oxidation states of +2 and +3 in its compounds.
Scandium (Sc): Scandium primarily shows an oxidation state of +3 and does not commonly exhibit any other stable oxidation states in its compounds.
Titanium (Ti): Titanium can exhibit multiple oxidation states, commonly +2, +3, and +4.
Nickel (Ni): Nickel commonly shows oxidation states of +2 and +3.
Conclusion:
Scandium is the only element among the options that shows only one stable oxidation state (+3) other than its elemental form. The correct answer is Option (2).
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Approach Solution -2
Step 1: About Scandium.
Scandium (Sc) is a transition metal with atomic number 21, located in Group 3 of the periodic table. It is a silvery-white metal and exhibits chemical properties similar to rare-earth elements.
Step 2: Oxidation State of Scandium.
- Scandium predominantly shows only one oxidation state in its compounds: +3.
- Unlike many other transition metals that show multiple oxidation states, scandium's chemistry is mostly restricted to +3.
- In its elemental form, scandium is in the 0 oxidation state.
Step 3: Reason for single oxidation state.
- This is because scandium has an electronic configuration of [Ar] 3d¹4s².
- The +3 state corresponds to loss of all three valence electrons (two 4s and one 3d), yielding a stable configuration.
- Higher or lower oxidation states are energetically unfavorable and hence not commonly observed.
Step 4: Comparison with other elements.
- Other transition metals often exhibit variable oxidation states due to involvement of d electrons.
- Scandium’s limited variable oxidation states make it unique in this aspect among the first-row transition metals.
Final Answer:
The element which shows only one oxidation state other than its elemental form is:
\[
\boxed{\text{Scandium}}
\]
