In all these molecules O2andNO, is stabilized by removal of electrons because it is having electrons in the anti-bonding orbital. And thus removal of electron from the anti bonding orbital, increases the bond order of O2andNO. And thus is becomes more stable after removal of electrons. Bond order of O2+is 2.5 and it is more than that of O2 which is having bond order as 2. Similarly Bond order of NOis2.5andthatofNO+is3.