Question

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

• A. Cobalt
• B. Scandium
• C. Titanium
• D. Nickel

Answer 1

The Correct Option is B

Analyzing Oxidation States of Each Element:

• 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).

Answer 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:
\[ \boxed{\text{Scandium}} \]