How will you obtain mercury from cinnabar ? 

Cinnabar ($HgS$ -mercury (II) sulphide or mercury sulphide ) is an ore of mercury. It is heated in air to give mercuric oxide $(HgO)$ . Mercuric oxide is further heated to get mercury . The reactions involved are, 

$2HgS(s)+3O_2(g)\stackrel{heat}{\to }2HgO(s)+2S{O}_2(g)$ 

$2HgO(s)\stackrel{heat}{\to }2Hg(s)+O_2(g)$