JAMB - Chemistry (1979 - No. 33)
the vapour density of a gas may be defined as
the mass of a unit volume of the gas compared to an equal volume of water vapour
the mass of a unit volume of the gas compared to an equal volume of hydrogen
the mass of a unit volume of the gas compared to an equal volume of oxygen
the mass of a unit volume of the gas minus the vapour pressure of water
two times the relative molecular mass of the gas