Question

Choose the statements which are incorrect in the case of Lanthanoids.

• A. Ce\(^{4+}\) is diamagnetic while Sm\(^{3+}\) is paramagnetic.
• B. The atomic size of the transition metals having atomic number greater than 71 are very close to that of the elements above them.
• C. Lanthanoids react with hot water forming water soluble \( \text{Ln(OH)}_3 \) with the liberation of \( \text{O}_2 \).
• D. The general electronic configuration of Lanthanoids is \( (n - 2)f^1_{14}d^0 6s^2 \), where \( n = 6 \).

Hint:

Lanthanoids are known for their similar properties, such as the stable oxidation states and the near-constant atomic sizes among the heavier elements in the series. Pay attention to the common oxidation states and their magnetic properties when analyzing lanthanoids.

Answer 1

The Correct Option is A

Step 1: Analyze Statement A.
The statement says "Ce\(^{4+}\) is diamagnetic while Sm\(^{3+}\) is paramagnetic." This is incorrect. Ce\(^{4+}\) is diamagnetic, but Sm\(^{3+}\) is also diamagnetic, not paramagnetic. Sm\(^{3+}\) has a stable 4f$^$5 configuration, which makes it diamagnetic, so this statement is false.

Step 2: Analyze Statement B.
The atomic size of the transition metals with atomic numbers greater than 71 is very close to that of the elements above them. This is a true statement. The atomic size of the lanthanoids is almost similar to that of the transition elements above them, with only a slight decrease in size as you move down the lanthanoid series due to the poor shielding of the 4f electrons.

Step 3: Analyze Statement C.
The statement says "Lanthanoids react with hot water forming water-soluble \( \text{Ln(OH)}_3 \) with the liberation of \( \text{O}_2 \)." This is true. Lanthanoids such as cerium, lanthanum, and others do react with hot water to form lanthanum hydroxide (\( \text{Ln(OH)}_3 \)), and oxygen gas is released during the reaction.

Step 4: Analyze Statement D.
The general electronic configuration of lanthanoids is given as \( (n - 2)f^1_{14}d^0 6s^2 \), where \( n = 6 \). This is a correct statement. Lanthanoids follow this general electronic configuration pattern, where the 4f orbitals are filled with electrons.

Step 5: Conclusion.
Since statement A is incorrect, the correct answer is option (A).