Hydrogen chloride gas may be prepared by addition of concentrated sulfuric acid (an oily, dense and corosive liquid) to sodium chloride (common salt). $H_2SO_4$ $+$ $NaCl$ $\longrightarrow$ $NaHSO_4$ $+$ $HCl$ The other product of this reaction is sodium hydrogensulfate, a white solid substance.
Hydrogen chloride gas is a colourless and fairly heavy gas with a pungent odour who condenses water vapour present in the air by dissolution and produces a kind of fog.