Question: how many molecules are in a gram?
Answer: A mass in grams numerically equal to the molecular weight contains one mole of molecules, which is known to be 6.02 x 10^23 (Avogadro's number). So if you have x grams of a substance, and the molecular weight is y, then the number of moles n = x/y and the number of molecules = n multiplied by Avogadro's number.