Official Correct Choice:
Option B: \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1, 3d^5 \)
Concept: Half-filled (\(d^5\)) and fully-filled (\(d^{10}\)) subshells offer extra thermodynamic exchange energy and spherical symmetry, making them exceptionally stable.
Formula: None required.
Solution: - Chromium has an atomic number \( Z = 24 \).
- The expected Aufbau configuration is \( [Ar] 4s^2 3d^4 \).
- However, to achieve the highly stable half-filled \(d\)-subshell, one electron is promoted from the \(4s\) orbital to the \(3d\) orbital.
- The actual configuration is anomalous: \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1, 3d^5 \).
Why other options are incorrect: Option A assumes rigid adherence to Aufbau without accounting for half-filled stability. Options C and D have incorrect total electron counts.
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