The number of paired electrons in $O_2$ molecule is  

$O_2\left(16e^{-}\right):\sigma 1s^2{\sigma }^{\ast }1s^2\sigma 2s^2{\sigma }^{\ast }2s^2\sigma 2P_z^2$
${{\pi }_{2px}}^2={{\pi }_{2py}}^2{{\pi }_{2px}^{\ast }}^1={{\pi }_{2py}^{\ast }}^1$
14 paired electrons, 2 unpaired electrons