Question

Which of the following statements regarding lanthanoids is correct?

• A. Basicity of lanthanoid hydroxides increases from \(La(OH)_3\) to \(Lu(OH)_3\)
• B. Atomic radii increase regularly from La to Lu
• C. Lanthanoid contraction is mainly due to poor shielding by \(4f\) electrons
• D. Cerium exhibits only the \(+3\) oxidation state

Hint:

Poor shielding by \(4f\) electrons is responsible for lanthanoid contraction, which causes decreasing atomic size and basicity across the series.

Answer 1

The Correct Option is C

Concept: Lanthanoid contraction refers to the gradual decrease in atomic and ionic radii across the lanthanoid series. This phenomenon has far-reaching consequences on the chemistry of lanthanoids and transition elements.

Step 1: Understand the cause of lanthanoid contraction. As atomic number increases from La to Lu, electrons are added to the \(4f\) subshell. The \(4f\) electrons provide poor shielding against nuclear charge. Consequently, the effective nuclear charge experienced by outer electrons increases. \[ Z_{eff}\uparrow \] leading to \[ \text{Atomic radius}\downarrow \]

Step 2: Examine option A. Basicity decreases from La to Lu because ionic size decreases. Therefore, \[ La(OH)_3 \] is more basic than \[ Lu(OH)_3 \] Hence option A is incorrect.

Step 3: Examine option B. Atomic radii decrease, not increase. Hence option B is incorrect.

Step 4: Examine option D. Cerium commonly exhibits: \[ +3 \] and \[ +4 \] oxidation states. Therefore option D is incorrect.

Step 5: The correct statement is: \[ \boxed{\text{Option C}} \]