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Question #44890

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The Question

Consider the chemical consequences of the lanthanoid contraction on the f-block and post-lanthanoid transition elements. Which of the following statements is \textbf{INCORRECT}?

Options

A.
The basic strength of $\ce{Ln(OH)3}$ decreases from $\ce{La(OH)3}$ to $\ce{Lu(OH)3}$ because the lanthanoid contraction increases the polarizing power of $\ce{Ln^{3+}}$ , enhancing the covalent character of the $\ce{Ln-OH}$ bond.
B.
Due to the lanthanoid contraction, $\ce{Hf^{4+}}$ has a nearly identical ionic radius to $\ce{Zr^{4+}}$ but a higher effective nuclear charge, which increases its polarizing power and makes $\ce{HfO2}$ less basic than $\ce{ZrO2}$ .
C.
The maximum polarizing power among the lanthanoids is observed for $\ce{Lu^{3+}}$ , rendering $\ce{Lu(OH)3}$ the least basic in the series and imparting it with a slight amphoteric character.
D.
The lanthanoid contraction is caused by the imperfect shielding of one $4f$ electron by another, which is less effective than the mutual shielding of $d$ electrons, leading to anomalously high densities for the 5d transition metals.

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Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

F-block Basic Character|Post-Lanthanoid Radii Equality|Carboxylic Acid Strength

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to differentiate between the application of Fajan's Rules within the f-block (where size dictates the basicity trend) and the post-lanthanoid d-block elements (Zr vs Hf).

Students often fall into the trap of 'Post-Lanthanoid Radii Equality', assuming that because Hf has the same size as Zr but a higher effective nuclear charge, it must be more polarizing and therefore its oxide must be less basic.

The hidden variable is that down Group 4, electronegativity actually decreases, making the Hf-O bond more ionic.

Thus, the general group trend prevails, and HfO2 is more basic than ZrO2, defying the simplistic polarization prediction.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	D and F Block Elements - Class 12
Concept	F-block Basic Character
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free