Question

Identify the correct statements about lanthanoids
I. \(\text{Ce}^{4+}\) and \(\text{Tb}^{4+}\) act as oxidising agents
II. \(\text{Eu}^{2+}\) and \(\text{Yb}^{2+}\) act as oxidising agents
III. Mischmetal is an alloy of 95% iron and 5% lanthanoid metal
IV. \(\text{La}^{3+}\) and \(\text{Ce}^{4+}\) are diamagnetic in nature

• A. I & II only
• B. I & IV only
• C. II, III & IV only
• D. I, II & IV only

Hint:

Lanthanoid Stability Rule: All ions strive for the +3 state. +4 ions \(\rightarrow\) Gain \(e^-\) \(\rightarrow\) Oxidising Agents. +2 ions \(\rightarrow\) Lose \(e^-\) \(\rightarrow\) Reducing Agents.

Answer 1

The Correct Option is B

Step 1: Understanding the Statement I: The most stable oxidation state for Lanthanoids is +3. Elements in +4 state (like \(\text{Ce}^{4+}\) and \(\text{Tb}^{4+}\)) tend to accept an electron to revert to the stable +3 state. Thus, they act as oxidising agents. Statement I is Correct.
Step 2: Understanding the Statement II: Elements in +2 state (like \(\text{Eu}^{2+}\) and \(\text{Yb}^{2+}\)) tend to lose an electron to achieve the stable +3 state. Thus, they act as reducing agents, not oxidising agents. Statement II is Incorrect.
Step 3: Understanding the Statement III: Mischmetal is an alloy consisting of a lanthanoid metal (~95%) and iron (~5%) and traces of S, C, Ca, and Al. The statement reverses the percentages (95% iron). Statement III is Incorrect.
Step 4: Understanding the Statement IV: Electronic Configuration of La (Z=57): \([\text{Xe}] 5d^1 6s^2\). \(\text{La}^{3+}\) configuration: \([\text{Xe}] 4f^0\). No unpaired electrons \(\rightarrow\) Diamagnetic. Electronic Configuration of Ce (Z=58): \([\text{Xe}] 4f^1 5d^1 6s^2\). \(\text{Ce}^{4+}\) configuration: \([\text{Xe}] 4f^0\). No unpaired electrons \(\rightarrow\) Diamagnetic. Statement IV is Correct. Conclusion: Only statements I and IV are correct.
Required Answer: Option (B).