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MHT CET202522 Apr 2025Morning ShiftChemistryd and f Block ElementsActual

Identify a weakest base from following

Options

  1. AEu ( OH )₃
  2. BLa ( OH )₃
  3. CLu ( OH )₃
  4. DGd ( OH )₃

Correct answer

C. Lu ( OH )₃

Step-by-step solution

The basicity of lanthanide hydroxides decreases across the series from La to Lu due to lanthanide contraction. This phenomenon results from poor 4f electron shielding, increasing effective nuclear charge and reducing ionic radii. A smaller M ³⁺ ionic radius corresponds to higher charge density, strengthening attraction to OH ^- ions. This increased covalent character in M - OH bonds reduces hydroxide ion dissociation, thereby decreasing basicity. The ionic radii order is La ³⁺ > Eu ³⁺ > Gd ³⁺ > Lu ³⁺ , so hydroxide

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