AP Chemistrymediummcq1 pt

The electron configuration of Cr (chromium, Z=24) is an exception to the Aufbau principle. Its configuration is:

A.[Ar]4s²3d³

B.[Ar]4s¹3d⁵

C.[Ar]4s⁰3d⁶

D.[Ar]4s²3d⁴

Explanation

Core Concept

Chromium is an exception: it promotes one 4s electron to the 3d subshell to achieve a half-filled d subshell ([Ar]4s¹3d⁵), which is more stable due to reduced electron-electron repulsion and symmetrical distribution.

Correct Answer

B[Ar]4s¹3d⁵

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