Chemistry Transition Elements UHS 2023
PMDC Verified Question 15 of 68
Which of the following electronic configuration is correct for \( ^{24}Cr \)?
A
\( 1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{6}, 4s^{1}, 3d^{5} \)
B
\( 1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{6}, 4s^{2}, 3d^{4} \)
C
\( 1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{6}, 3d^{6} \)
D
\( 1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{6}, 4f^{6} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: \( 1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{6}, 4s^{1}, 3d^{5} \)
Concept:

Chromium is notorious for its anomalous electron configuration, prioritizing a half-filled \(d\)-subshell for extra stability.

Solution:

  • The first 18 electrons fill the core shells: \(1s^2 \; 2s^2 \; 2p^6 \; 3s^2 \; 3p^6\).


  • For the remaining 6 valence electrons, the standard filling rule would predict \(4s^2 \; 3d^4\).


  • However, moving one electron from \(4s\) to \(3d\) results in \(4s^1 \; 3d^5\). This configuration gives exactly one electron to each of the five \(d\)-orbitals.


  • This perfectly symmetrical half-filled state minimizes electron repulsion, making \(4s^1 \; 3d^5\) the correct ground state configuration.


Why other options are incorrect:

  • Option B: The theoretically expected, but incorrect configuration.


  • Option D: F-orbitals do not begin filling until much higher atomic numbers.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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