Number of paired electrons in $${O_2}$$  molecule is :

Solution :
$${O_2} = $$  Oxygen $$\left( {Z = 8} \right)$$  has following molecular orbital configuration of $${O_2}.$$
$${O_2}\left( {16{e^ - }} \right) = \sigma 1{s^2},{\sigma ^ * }1{s^2},\sigma 2{s^2},$$       $${\sigma ^ * }2{s^2},\sigma 2p_x^2,\left\{ {\pi 2p_y^2 = \pi 2p_z^2,} \right.$$     $$\left\{ {{\pi ^ * }2p_y^1 = {\pi ^ * }2p_z^1} \right.$$    i.e., 2 unpaired and 14 paired electrons.