According to MOT, lowest unoccupied molecular orbital (LUMO) in O2- is

O2-2-KK'σ2s2σ2s*2σ2pz2π2px2π2py2π2px*2π2py*2O2--KK'σ2s2σ 2s*2σ2pz2π2py2π2py2π2px*2π2py*1O2 -KK'σ2s2σ2s*2σ2pz2π2px2π2py2π2px*1π2py*1O2+-KK'σ2s2σ2s*2σ2pz2π2px2π2py2π2px*1π2py*0Bond order and magnetic moment :μs=nn+2 B. M ; O2-2=10-82=1; Diamagnetic...μs=0 ; O2-=10-72=1.5; Paramagnetic..μs=1.732 B.M ; O2=10-62=2; Paramagnetic.......μs=2.82 B.M ; O2+=10-52=2.5; Paramagnetic.....μs=1.732B.M  ;O — O bond length inO2-2>O2->O2>O2+