How many unpaired electrons are present in an oxide ion?

An oxide ion (O²⁻) has gained two electrons compared to a neutral oxygen atom. A neutral oxygen atom has six valence electrons and is configured as 1s² 2s² 2p⁴. When it gains two electrons to form O²⁻, it fills its 2p subshell, resulting in the electron configuration 1s² 2s² 2p⁶. Therefore, the oxide ion has no unpaired electrons.