Which of the following is the correct electron configuration for the oxide ion, O^{2-}?

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

Answer: (C)

Verified step by step guidance

1. Step 1: Identify the atomic number of oxygen (O), which is 8. This means a neutral oxygen atom has 8 electrons.
2. Step 2: Understand that the oxide ion, O^{2-}, has gained 2 extra electrons, so the total number of electrons is 8 + 2 = 10.
3. Step 3: Write the electron configuration for 10 electrons by filling the orbitals in order of increasing energy: 1s, 2s, then 2p.
4. Step 4: Fill the 1s orbital with 2 electrons, the 2s orbital with 2 electrons, and the 2p orbitals with the remaining 6 electrons.
5. Step 5: Conclude that the correct electron configuration for O^{2-} is \$1s^2 2s^2 2p^6$, which corresponds to a full 2p subshell.