1) relative molecular mass is the ratio of the average mass of only 1 molecule of an element to 1/12 of the mass of that particular substance of the atom.
2) gram molecular mass is a mass in grams that is numerically equal to the molecular weight of a substance.
3) vapour density is the density of a vapour that is relative to that of hydrogen at the same time.
4) the relative atomic mass is the same as that of relative molecular mass.
5) a mole is a chemical mass unit that is defined to be 6.022* 10 to the power 23 atoms, molecules,etc.
6) we can find atomicity of elements by the number of atoms that is constituting a molecule is known as its atomicity. that is on the basis of the atoms that are present in that elment or substance.
hope this helps u !!!!!!!!