Question

Assertion: $La(OH{)}_3$ is the most basic, while $Lu(OH{)}_3$ is the least basic.

Reason: As the size of lanthanoids decreases, covalent character of hydroxides decreases and basic character increases.

• A. If both assertion and reason are true and reason is the correct explanation of assertion.
• B. If both assertion and reason are false.
• C. If both assertion and reason are true but reason is not the correct explanation of assertion.
• D. If assertion is true but reason is false.

Answer 1

The correct option is D If assertion is true but reason is false.

The basic strength of hydroxides is $La(OH{)}_3>Lu(OH{)}_3$. Due to lanthanide contraction, size of $M^{3+}$ ions decreases and there is an increase in the covalent character of $M-OH$ bond. (Small cation, more is covalent character - Fajan’s rule).
Option (c) is correct