Question

Number of unpaired electron(s) in $O_2{}^{-}$ is/are:

Answer 1

The electronic configuration of the $O_2{}^{-}$ ion containing 17 electrons can be written as:

$1s^{2}1s^{2}2s^{2}2s^{2}2p{z}^{2}2p{x}^{2}2p{y}^{2}p{x}^{2}2p{y}^1$

It has one unpaired electron in anti bonding $\pi$ orbitals.