Question:
According to molecular orbital theory, the number of unpaired electron(s) in $\mathrm{O}_{2}^{2-}$ is :
Solution:
Molecular orbital configuration of $\mathrm{O}_{2}^{2-}$ is
$\sigma_{1 \mathrm{~s}}^{2} \sigma_{1 \mathrm{~s}}^{* 2} \sigma_{2 \mathrm{~s}}^{2} \sigma_{2 \mathrm{~s}}^{* 2}\left(\pi 2 \mathrm{p}_{\mathrm{x}}^{2}=\pi 2 \mathrm{p}_{\mathrm{y}}^{2}\right)\left(\pi_{2 \mathrm{px}}^{* 2}=\pi_{2 \mathrm{py}}^{* 2}\right)$
Zero unpaired electron