Dioxygen is paramagnetic. According to molecular orbital theory this is because

1. Aall its electrons are paired in bonding orbitals
2. Bit has two unpaired electrons in the ${\sigma }_{2p}$ orbital
3. Cit has two unpaired electrons in the degenerate ${\pi }^{\ast }$ orbitals
4. Dit has one unpaired electron in a ${\sigma }^{\ast }$ orbital