Those species which have unpaired electrons are called paramagnetic species. And those species which have no unpaired electrons are called diamagnetic species. (a) O22− has 18 electrons. Moleculer orbital configuration of O22− is σ1s2σ1s2*σ2s2σ2s2*σ2pz2π2px2=π2py2π2px2*=π2py2* Here is no unpaired electron so it is diamagnetic. (b) NO has 15 electrons. Moleculer orbital configuration of NO is σ1s2σ1s2*σ2s2σ2s2*σ2pz2π2pz2=π2py2π2px1*=π2py0* Here is 1 unpaired electron, So it is Paramagnetic. (c) O2 has 16 electrons. Moleculer orbital configuration of O2 is σ1s2σ1s2*σ2s2σ2s2*σ2pz2π2pz2=π2py2π2px1*=π2py1* Here 2 unpaired electron present, so it is paramagnetic. (d) O2+has 15 electrons. Moleculer orbital configuration of O2+is σ1s2σ1s2*σ2s2σ2s2*σ2pz2π2pz2=π2py2π2px1*=π2py0* Here 1 unpaired electron present, so it is paramagnetic.