Question

Number of colourless lanthanoid ions among the following is ____.
\[ \text{Eu}^{3+}, \, \text{Lu}^{3+}, \, \text{Nd}^{3+}, \, \text{La}^{3+}, \, \text{Sm}^{3+} \]

Answer 1

Correct Answer: 2

Step 1: Analyze electronic configurations

1. La³⁺: [Xe]4f⁰ (No unpaired electrons, colourless).
2. Lu³⁺: [Xe]4f¹⁴ (No unpaired electrons, colourless).
3. Nd³⁺: [Xe]4f³ (Unpaired electrons, coloured).
4. Sm³⁺: [Xe]4f⁵ (Unpaired electrons, coloured).
5. Eu³⁺: [Xe]4f⁶ (Unpaired electrons, coloured).

Step 2: Count colourless ions

Lanthanide ions that are colourless: La³⁺ and Lu³⁺.

Final Answer: 2.