Which from following pair of elements have one electron in 5d-subshell in observed electronic configuration?

Which from following pair of elements have one electron in 5d-subshell in observed electronic configuration?
  1. $\operatorname{Sm}(Z=62)$ and $\operatorname{Eu}(Z=63)$
  2. $\mathrm{Lu}(\mathrm{Z}=71)$ and $\mathrm{Dy}(\mathrm{Z}=66)$
  3. Gd $(Z=64)$ and $\mathrm{Lu}(\mathrm{Z}=71)$
  4. $\mathrm{Ce}(\mathrm{Z}=58)$ and $\mathrm{Nd}(\mathrm{Z}=60)$

Solution

$\begin{aligned} & \mathrm{Ce}(58)=[\mathrm{Xe}] 4 \mathrm{f}^1 5 \mathrm{~d}^1 6 \mathrm{~s}^2 \\ & \mathrm{Nd}(60)=[\mathrm{Xe}] 4 \mathrm{f}^4 6 \mathrm{~s}^2 \\ & \mathrm{Sm}(62)=[\mathrm{Xe}] 4 \mathrm{f}^6 6 \mathrm{~s}^2 \\ & \mathrm{Eu}(63)=[\mathrm{Xe}] 4 \mathrm{f}^7 6 \mathrm{~s}^2 \\ & \mathrm{Dy}(66)=[\mathrm{Xe}] 4 \mathrm{f}^{10} 6 \mathrm{~s}^2 \\ & \mathrm{Gd}(64)=[\mathrm{Xe}] 4 \mathrm{f}^7 5 \mathrm{~d}^1 6 \mathrm{~s}^2\end{aligned}$

Asked in: MHT CET 2022 (05 Aug Shift 1)

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