the vapour density of a gas may be defined as
-
A.
the mass of a unit volume of the gas compared to an equal volume of water vapour -
B.
the mass of a unit volume of the gas compared to an equal volume of hydrogen -
C.
the mass of a unit volume of the gas compared to an equal volume of oxygen -
D.
the mass of a unit volume of the gas minus the vapour pressure of water -
E.
two times the relative molecular mass of the gas