Question

Oxygen has no unpaired electron but still it is para-magnetic.Why?

Answer 1

Theory predicts that O2 has two unpaired electrons in 2Px and 2Py degenerate oribitals.Unpaired electrons spin in the same direction as each other, which increases the magnetic field effect. So O2 becomes paramagnetic.

Answer 2

The reason that it is paramagnetic is because the oxygen molecule has two unpaired electrons. ... Note that according to Valence Shell Electron Pair Repulsion theory , O2 has no unpaired electrons but according to Molecular Orbital (MO) theory it does have unpaired electrons.