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

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.