AP Chemistryeasymcq1 pt
What is the ground-state electron configuration of a potassium atom (Z = 19) in noble-gas shorthand?
A.[Ar] 4s¹
B.[Ar] 3d¹
C.[Ne] 4s² 3p⁵
D.[Kr] 4s¹
Explanation
Core Concept
Potassium's first 18 electrons fill through argon, and the nineteenth enters the 4s orbital. In the buildup after argon, 4s sits lower in energy than 3d, so filling order places it next. That lone 4s electron is what makes potassium a reactive Group 1 metal.
Correct Answer
A[Ar] 4s¹
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