Question

Explain paramagnetic character of oxygen molecule with the help of mo diagram

Answer 1

The paramagnetic character of oxygen came through unpaired electron which could not be explained by any theory but molecular orbital theory. On the enclosed molecular orbitals diagram of the oxygen molecule, one can see two unpaired electrons on the $\pi*_{2p_x}$ and $\pi*_{2p_y}$. Hund’s first rule dictates that one electron occupies each orbital, and their spins are parallel, giving the $O_2$  molecule two unpaired electrons. This phenomenon is making it paramagnetic.