The number of antibonding electron pairs in $O_2^{2-}$ molecular ion on the basic of molecular orbital theory is

Total number of electrons in $O_2^{2-}$ =16+2=18
According to MOT, the configuration of $O_2^{2-}$ is $\sigma 1s^2,\stackrel{\star }{\sigma }1s^2,\sigma 2s^2,\stackrel{\star }{\sigma }2s^2,\sigma 2p_x^2,\pi 2p_y^2\approx \pi 2p_z^2,\stackrel{\star }{2}{p}_y^2\approx \stackrel{\star }{\pi }2p_z^2$
So, the number of antibonding electron pairs =4