Chemistry Transition Elements UHS 2024
PMDC Verified Question 2 of 68
Electronic configuration of chromium (proton number 24) is:
A
\( [Ar], 3d^{4}, 4s^{2} \)
B
\( [Ar], 3d^{5}, 4s^{1} \)
C
\( [Ar], 3d^{5}, 4s^{2} \)
D
\( [Ar], 3d^{6}, 4s^{2} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( [Ar], 3d^{5}, 4s^{1} \)
Concept:

Chromium is a classic exception to standard Aufbau filling rules. It adopts a configuration that maximizes thermodynamic stability.

Solution:

  • Chromium (\(Z=24\)) has an Argon core (18 electrons), leaving 6 valence electrons to place.


  • Standard filling predicts \(4s^2 \; 3d^4\).


  • However, moving one electron from the \(4s\) orbital into the \(3d\) orbital creates a \(3d^5\) state.


  • A \(3d^5\) configuration means the \(d\)-subshell is exactly half-filled, making it perfectly symmetrical. This symmetry minimizes electrostatic repulsion and maximizes exchange energy, rendering it highly stable.


  • Therefore, the correct configuration is \([Ar] \; 3d^5 \; 4s^1\).


Why other options are incorrect:

  • Option A: The expected but incorrect configuration.


  • Option C/D: These correspond to Manganese (\(Z=25\)) and Iron (\(Z=26\)) respectively.

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.

Previous Question All Transition Elements MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App