How many orbitals are completely filled in an atom of calcium (Z = 20)?
A8
B9
C10CORRECT
D7
GCEChemistryAtomic Structure and Periodicity2024
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Why the answer is C, and why the others tempt you.
Calcium's configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². Counting filled orbitals: 1s(1) + 2s(1) + 2p(3) + 3s(1) + 3p(3) + 4s(1) = 10 completely filled orbitals, each containing 2 electrons accounting for all 20 electrons. Every orbital listed is fully occupied.
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