MCAT Chemistry Question — Electron Configuration

What is the electron configuration of calcium in CaCl₂?

A) 1s²2s²2p⁶3s²3p⁵

B) 1s²2s²2p⁶3s²3p⁶

C) 1s²2s²2p⁶3s²3p⁶4s¹

D) 1s²2s²2p⁶3s²3p⁶4s²

Explanation

This question asks the examinee to determine the electron configuration of the calcium ion, as it exists in calcium chloride. Calcium in its elemental state has a total of 20 electrons. Therefore Ca²⁺ has a total of 18 electrons. In the answer choices provided, choice B is the only electron configuration that contains 18 electrons making B the correct answer.

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