Question

what electron configuration matches an oxygen ion (o²⁻)?
1s²2s²2p⁴
1s²2s²2p⁶3s2, 3p⁶4s²3d¹⁰4p⁵
1s²2s²2p⁶3s²3p⁶4s²3d¹
1s²2s²2p⁶

Explanation:

Step1: Determine O atom's electrons

Oxygen (O) has an atomic number of 8, so a neutral O atom has 8 electrons. The electron configuration of neutral O is $1s^2 2s^2 2p^4$.

Step2: Analyze O²⁻ ion

The $O^{2-}$ ion has gained 2 electrons, so it has $8 + 2 = 10$ electrons.

Step3: Check electron configurations

• First option: $1s^2 2s^2 2p^4$ has 8 electrons (neutral O), incorrect.
• Second option: The configuration has many more electrons (sum the exponents: $2 + 2 + 6 + 2 + 6 + 2 + 10 + 5 = 35$), incorrect.
• Third option: Sum of exponents is more than 10, incorrect.
• Fourth option: $1s^2 2s^2 2p^6$ has $2 + 2 + 6 = 10$ electrons, which matches $O^{2-}$.

Answer:

The option with electron configuration $1s^2 2s^2 2p^6$ (the fourth option in the display).