Which of the following represents the ground-state electron configuration of the oxide ion, O^{2-}?

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

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 compared to the neutral oxygen atom, so it has a total of 8 + 2 = 10 electrons.
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: Recall the maximum number of electrons each subshell can hold: 1s can hold 2, 2s can hold 2, and 2p can hold 6 electrons.
5. Step 5: Combine these to write the full ground-state electron configuration for O^{2-} as \$1s^2 2s^2 2p^6$, which corresponds to a filled 2p subshell.