Q30 / 160 · TS EAMCET 2024 (11 May Shift 1) · Chemistry

Observe the following $f$-block elements $\mathrm{Eu}(Z=63) ; \mathrm{Pu}(Z=94) ; \mathrm{Cf}(\mathrm{Z}=98) ; \mathrm{Sm}(\mathrm{Z}=62) ; \mathrm{Gd}$ $(\mathrm{Z}=64) ; \mathrm{Cm}(\mathrm{Z}=96)$ How many of the above have half-filled $f$-orbitals in their ground state?

  • Correct answer
    A
    $3$
  • B
    $4$
  • C
    $2$
  • D
    $5$

Solution

$\begin{array}{|c|c|c|} \hline \begin{array}{c} \text { Atomic } \\ \text { Number } \end{array} & \text { f-Block element } & \text { Electronic configuration } \\ \hline 63 & \mathrm{Eu} & {[\mathrm{Xe}] 4 \mathrm{f}^7 6 \mathrm{~s}^2} \\ \hline 94 & \mathrm{Pu} & {[\mathrm{Rn}] 5 \mathrm{f}^6 7 \mathrm{~s}^2} \\ \hline 98 & \mathrm{Cf} & {[\mathrm{Rn}] 5 \mathrm{f}^{10} 7 \mathrm{~s}^2} \\ \hline 62 & \mathrm{Sm} & {[\mathrm{Xe}] 4 \mathrm{f}^6 6 \mathrm{~s}^2} \\ \hline 64 & \mathrm{Gd} & {[\mathrm{Xe}] 4 \mathrm{f}^7 5 \mathrm{~d}^1 6 \mathrm{~s}^2} \\ \hline 96 & \mathrm{Cm} & {[\mathrm{Rn}] 5 \mathrm{f}^7 6 \mathrm{~d}^1 7 \mathrm{~s}^2} \\ \hline \end{array}$ $\mathrm{So} \mathrm{Eu}, \mathrm{Gd}$ and Cm have half-filled f-orbitals.

Hence, the correct answer is option: 'A'.

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