Which of the following is the ground state electron configuration for a Ca^{2+} ion?

• A. 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2
• B. 1s^2 2s^2 2p^6 3s^2 3p^6
• C. 1s^2 2s^2 2p^6 3s^2 3p^4
• D. 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of calcium (Ca), which is 20, meaning a neutral Ca atom has 20 electrons.
2. Write the ground state electron configuration for neutral Ca: \$1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2$.
3. Recognize that a Ca^{2+} ion has lost 2 electrons compared to neutral Ca, so it has 18 electrons.
4. Remove the 2 electrons from the highest energy level first, which is the 4s orbital, resulting in the configuration \$1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6$ for Ca^{2+}.
5. Confirm that this configuration corresponds to the electron configuration of the noble gas argon, indicating a stable, ground state configuration for Ca^{2+}.