JEE Main 2014 · 9 Apr · Shift 1, Chemistry question 46

Counting π* electrons:

• $\ce{N2}$ and $\ce{N2^2+}$: none;
• $\ce{O2^2-}$: four, paired;
• superoxide $\ce{O2-}$: three ($\pi^{*3}$), so one unpaired electron.