Answer
Please see the work below.
Work Step by Step
We know that the molecular orbital description of $O_2$ molecule is $KK(\sigma_2 *)^2 (\sigma_2 *)^2(\pi_{2p})^4(\sigma_{2p})^2(\pi_{2p}*)^2$.
In $\pi_{2p}*$ orbital, both the electrons should be in the same orbital for all electrons to be paired.