MHTCET 22 Apr 2025 Shift 1 Paper

Concept:Basicity of lanthanide hydroxides decreases across the series due to lanthanide contraction.Explanation:As we move from La to Lu, the ionic radius of $\mathrm{Ln}^{3+}$ decreases steadily.This increases the charge density and polarising power of the metal ion.Higher polarisation weakens the $\mathrm{O}-\mathrm{H}$ bond and reduces the ionic character of $\mathrm{Ln}(\mathrm{OH})_{3}$.Therefore, basic strength decreases from $\mathrm{La}(\mathrm{OH})_{3}$ to $\mathrm{Lu}(\mathrm{OH})_{3}$.Among the given options, La has the largest size, while Lu has the smallest size.Thus, $\mathrm{Lu}(\mathrm{OH})_{3}$ has the lowest basicity.Answer:$\mathrm{Lu}(\mathrm{OH})_{3}$ is the weakest base.Correct option: C.