Question

Choose the symbol of a lanthanoid metal which is well known to exhibit \(+4\) oxidation state.

• A. \(\mathrm{La}\)
• B. \(\mathrm{Th}\)
• C. \(\mathrm{Ce}\)
• D. \(\mathrm{Cm}\)

Hint:

Among lanthanoids, Cerium commonly shows \(+4\) oxidation state while Europium often shows \(+2\) oxidation state due to extra electronic stability.

Answer 1

The Correct Option is C

Concept: Lanthanoids generally exhibit the +3 oxidation state. However, a few lanthanoids can also show other oxidation states because of the extra stability associated with empty, half-filled, or completely filled \(4f\)-subshells.

Step 1: Recall the common oxidation state of lanthanoids.
The most common oxidation state of lanthanoids is: \[ +3 \] This corresponds to the removal of two \(6s\) electrons and one \(5d\) or \(4f\) electron.

Step 2: Identify lanthanoids showing \(+4\) state.
Cerium exhibits the oxidation state: \[ Ce^{4+} \] because removal of one additional electron gives the stable configuration: \[ [Xe] \] which corresponds to an empty \(4f\)-subshell.

Step 3: Examine the options.

• La generally exhibits only \(+3\) state.
• Th is an actinoid, not a lanthanoid.
• Ce is a lanthanoid well known for its \(+4\) oxidation state.
• Cm is also an actinoid.

Step 4: Final answer.
\[ \boxed{\mathrm{Ce}} \]