H2+and He2+contains odd number of electrons ∴ They are paramagnetic. Among Li2 and O2 Li2(6)=σ1s2,σ*1s2,σ2s2 Li have no unpaired electron. ∴ It is diamagnetic O2(18)=σ1s2,σ1s2,σ2s2,σ2s2π2px2=π2py2 σ2pz2,π*2px1=π*2py1 It has two unpaired electrons. So, it is paramagnetic.