Compounds containing unpaired electrons are paramagnetic in nature, while compounds containing no unpaired electrons are diamagnetic in nature.
Attached is the molecular orbital diagram of S2 molecule. For the MOT diagram it can be seen that S2 molecule has two unpair electron in two π* orbital. Due to this, it is paramagnetic in nature.
In contrast to this, Li2, C2 and Cl2 have no unpaired electrons. Hence they are diamagnetic in nature.
