From ideal gas equation PV=nRT where n=m∕M So, PV=mRT∕M P=mRT∕MV P=dRT∕M ∵ At constant temperature and pressure, d∝M ∴d1∕d2=M1∕M2 (Here d1 and M1 aredensity and molecular mass of ammonia whereas d2 and M2 are density and molecular mass of hydrogen chloride) d1∕d2=17∕36.5:d1∕d2=0.46