Which configuration correctly represents a ground-state copper atom (Z = 29), an exception to the Aufbau order?
Correct answer C. [Ar] 3d¹⁰ 4s¹
Explanation
Copper is an exception to the Aufbau order: a completely filled 3d¹⁰ subshell is extra stable, so one 4s electron moves to 3d, giving [Ar] 3d¹⁰ 4s¹.
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