# Does peroxide ion have any unpaired electrons?

According to the MOT diagram there are no unpaired electrons but in an exam I gave the answer key said it has 2 unpaired electrons. I can also find some images on google where it has 2 unpaired electrons.

Which one is correct and why?

• @santimirandarp I believe, in the above MO, the BO is 2. – William R. Ebenezer May 17 '19 at 12:28
• @Random, peroxide is diamagnetic. So the provided MO is correct. Oxygen ($\ce{O2}$) has 2 unpaired electrons, but $\ce{O2^2-}$ hasn't. – William R. Ebenezer May 17 '19 at 12:31

The MO diagram you show is correct. $$O_2^{2-}$$ has a bond order of 1 (equivalent to a single bond between the two O atoms) as the antibonding $$\pi^*$$ orbitals contain 4 electrons and this cancels the $$\pi$$ orbitals' 4 bonding electrons. See the Mo diagrams for the different $$O_2$$ species below: