Paramagnetic species contains unpaired electrons in their molecular orbital electronic configuration. Molecular orbital configuration of the given species is as CO(6+8=14)=σ1s2,σ∗1s2,σ2s2,σ∗2s2,π2px2≈π2py2,σ2pz2 (All the electrons are paired so it is diamagneitc.) O2−(8+8+1=17)=σ1s2,σ∗1s2,σ2s2,σ∗2s2,σ2pz2,π2px2≈π2py2,π∗2px2≈π∗2py1 It contains one unpaired electron so it is paramagnetic. CN−(6+7+1=14)= same as CONO+(7+8−1)= same as CO Thus, among the given species only O2−is paramagnetic.