Assuming ideal gas behaviour, the ratio of density of ammonia to that of hydrogen chloride at same temperature and pressure is : (Atomic wt. of Cl = 35.5 u)

We know that, P =dRTM [ ∵d = density = mV ]at constant temperature and pressure d ∝ MNow let d1 and d2 are the density of ammonia and HCl.∴     d1d2=MNH3MHCl⇒d1d2 =1736.5 = 0.46