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

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

Answer: (A)

Verified step by step guidance

1. Step 1: Identify the atomic number of oxygen (O). Oxygen has an atomic number of 8, which 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 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: first the 1s orbital, then 2s, and then 2p orbitals.
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 electron configuration for O^{2-} as \$1s^{2} 2s^{2} 2p^{6}$, which corresponds to a filled 2p subshell.