As per Molecular orbital theory,
N2(14electrons) all paired electrons, so diamagnetic.
N2⇒σ1s2<σ∗1s2<σ2s2<σ∗2s2<π2px2=π2py2<σ2pz2
O3−24 electrons and diamagnetic.
CO(14electrons) all paired so, diamagnetic.
CO⇒σ1s2<σ∗1s2<σ2s2<σ∗2s2<π2px2=π2py2<σ2pz2
NO(15electrons) one unpaired electron so, paramagnetic.
NO⇒σ1s2<σ∗1s2<σ2s2<σ∗2s2<π2px2=π2py2<σ2pz2<π∗2px1=π∗2py0