In O2 molecule, two electrons are present in antibonding orbitals. O2(8+8=16)=σ1s2,σ*1s2,σ2s2σ*2s2σ22pz2,π2px2=π2py2,π*2px=π*2py1 Removal of one electron from the O2 molecule gives O2+ in which the number of antibonding electrons is one less and hence, BO increases. Thus, removal of one electron from O2 stabilises the molecule.