Many books show that we will fill them one by one (hunds rule) with increasing energy level(aufbau rule) but when filling comes to last antibonding orbitals , filling shows that we are pairing electrons. How can we pair electrons in antibonding orbitals? antibonding orbitals opposes bonding but pairing shows that it is supporting bonding. We can fill an already paired electrons but can't pair them in the antibonding electrons. So please tell me the correct way of filling the electrons.?