Moles measure quantity of substance. There is a subtle ambiguity about treating “moles” – whether as “mass” or “number”. We take the position that it measures “amount of substance”, which can be either be expressed in terms of mass or in terms of numbers. The two approaches are equivalent and need not be a source of ambiguity any further.

Some basic ideas of the mole concept :
1: Molecular weight is arithmetic sum of atomic weights of constituent atoms.
2: Atomic weight is expressed in “atomic mass unit (a.m.u)”.
3: The atomic mass unit is the mass equivalent to 1/12 mass of a C-12 atom

The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

1 mole of a substance = gram amt. / molecular mass(if it is compound) or atomic mass(if it is a element) of that substance