hydrogen chloride

Because the molar volume of gas is constant (24 litre per mol in 1 atm pressure and 25 degree celcius) so the density of gas is depend on the molecular weight of the gas. in air there are Approx.80% nitrogen which molecular weight about 28 and 20% oxygen which molecular weight is about 32 so the averaged molecular weight is about 29 to 30. Therefore, if a gas molecue which molecular weight is larger than 30, it will be sink when it release and most of the time use downward delivery to collect, and the molecualr weight HCl is about 36.