Which of the following is the correct electron configuration for the chloride ion, Cl⁻?

• A. 1s^2 2s^2 2p^6 3s^2 3p^3
• B. 1s^2 2s^2 2p^6 3s^2 3p^5
• C. 1s^2 2s^2 2p^6 3s^2 3p^6
• D. 1s^2 2s^2 2p^6 3s^2 3p^4

Answer: (C)

Verified step by step guidance

1. Identify the atomic number of chlorine (Cl), which is 17. This means a neutral chlorine atom has 17 electrons.
2. Understand that the chloride ion (Cl⁻) has gained one extra electron compared to the neutral atom, so it has 18 electrons in total.
3. Recall the order of filling electron orbitals according to the Aufbau principle: 1s, 2s, 2p, 3s, then 3p.
4. Write the electron configuration for 18 electrons by filling orbitals in order: 1s^2, 2s^2, 2p^6, 3s^2, and 3p^6.
5. Compare the given options to this configuration and select the one that matches the full 18-electron configuration for Cl⁻.