Question

The number of unpaired electrons in a diatomic molecule of an element with atomic number 8 is:

Answer 1

Element of Atomic number = 8 is oxygen, it has two unpaired $e^{-}$ in antibonding molecular orbital according to molecular orbital theory.

Electronic configuration of $O_2$ is:
$\sigma \left(1s{)}^2{\sigma }^{\ast }\right(1s{)}^2\sigma \left(2s{)}^2{\sigma }^{\ast }\right(2s{)}^2\sigma \left(2p_z{)}^2\pi \right(2p_x{)}^2\pi \left(2p_y{)}^2{\pi }^{\ast }\right(2p_x{)}^1{\pi }^{\ast }(2p_y{)}^1$