Assertion : La(OH)_3 is more basic than Lu(OH)_3 .Reason : Size of Lu^3+ increases and shows more covalent character.

Correct answer: (C) If assertion is true but reason is false. Due to lanthanide contraction, the size of Lu^3+ is decreased and therefore Lu(OH)_3 shows more covalent character (Small cation, more is covalent character - Fajan's rule). Thus La(OH)_3 is more ionic and thus more basic.

Q37 / 180 · AIIMS 2012 · Chemistry

Assertion : $\mathrm{La}(\mathrm{OH})_3$ is more basic than $\mathrm{Lu}(\mathrm{OH})_3$.Reason : Size of $\mathrm{Lu}^{3+}$ increases and shows more covalent character.

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

Solution

Due to lanthanide contraction, the size of $\mathrm{Lu}^{3+}$ is decreased and therefore $\mathrm{Lu}(\mathrm{OH})_3$ shows more covalent character (Small cation, more is covalent character - Fajan's rule). Thus $\mathrm{La}(\mathrm{OH})_3$ is more ionic and thus more basic.

Hence, the correct answer is option: 'C'.

Assertion : $\mathrm{La}(\mathrm{OH})_3$ is more basic than $\mathrm{Lu}(\mathrm{OH})_3$.Reason : Size of $\mathrm{Lu}^{3+}$ increases and shows more covalent character.

Solution

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