Q23 / 90 · JEE Main 2024 (09 Apr Shift 1) · Chemistry
Number of colourless lanthanoid ions among the following is ________
\(\mathrm{Eu}^{3+}, \mathrm{Lu}^{3+}, \mathrm{Nd}^{3+}, \mathrm{La}^{3+}, \mathrm{Sm}^{3+}\)
Correct answer: 2
Solution
$\begin{aligned}
& \mathrm{La}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^0 \\
& \mathrm{Nd}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^3 \\
& \mathrm{Sm}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^5 \\
& \mathrm{Eu}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^6 \\
& \mathrm{Lu}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^{14}
\end{aligned}$
$\mathrm{La}^{+3}$ and $\mathrm{Lu}^{+3}$ do not show any colour because no unpaired electron is present.
Hence, the correct answer is 2.