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

• A. 1s^2 2s^2 2p^6 3s^2 3p^4
• 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^3

Answer: (C)

Verified step by step guidance

1. Step 1: Identify the atomic number of chlorine (Cl), which is 17. This means a neutral chlorine atom has 17 electrons.
2. Step 2: Understand that the chloride ion (Cl⁻) has gained one extra electron, so it has 18 electrons in total.
3. Step 3: Write the electron configuration for 18 electrons by filling the orbitals in order of increasing energy: 1s, 2s, 2p, 3s, and 3p.
4. Step 4: Recall the maximum number of electrons each subshell can hold: 1s (2), 2s (2), 2p (6), 3s (2), and 3p (6).
5. Step 5: Combine these to write the full electron configuration for Cl⁻ as \$1s^2 2s^2 2p^6 3s^2 3p^6$, which corresponds to a filled 3p subshell.