Question

Identify the correct statement from the following.

• A. The green manganate ion shows diamagnetic nature but the permanganate ion exhibits paramagnetic nature
• B. Interstitial compounds of transition metals have lower melting points than that of pure transition metals and their compounds are chemically reactive
• C. Cerium is a lanthanoid metal which exists in a stable oxidation state of +4, besides exhibiting an oxidation state of +3
• D. Cr(VI) is more stable than W(VI) and hence acts as a good oxidizing agent

Hint:

In transition and lanthanoid chemistry, always be aware of the multiple oxidation states that some elements can adopt. Cerium is one such example where the \(+3\) and \(+4\) states are both stable.

Answer 1

The Correct Option is C

Let’s evaluate each option: 
1. Option (A): - The green manganate ion \((\text{MnO}_4^{2-})\) is paramagnetic, not diamagnetic. The permanganate ion \((\text{MnO}_4^{-})\) is also paramagnetic, not diamagnetic. Hence, this statement is incorrect. 
2. Option (B): - Interstitial compounds of transition metals do tend to have higher melting points than pure transition metals due to the presence of extra atoms that enhance the metallic bonding. Their compounds are usually less reactive. Thus, this statement is incorrect. 
3. Option (C): - Cerium (Ce) is a lanthanoid metal that exhibits a stable oxidation state of \(+4\) as well as the oxidation state of \(+3\). Cerium is unique because it can stabilize both these oxidation states, making this statement correct. 
4. Option (D): - Chromium (Cr) in the \(+6\) oxidation state is a strong oxidizing agent, while Tungsten (W) in the \(+6\) oxidation state is more stable. 
Thus, this statement is incorrect. Therefore, the correct statement is (C): Cerium exists in both +4 and +3 oxidation states, with the +4 oxidation state being the most stable.