Well, knowing that the molar mass of O2 is 32 g/mol. In 16 grams of pure O2, there is 0.5 mol of Oxygen - O2. In 48 grams there would be 0.5 • 3 which is 3/2 or 1.5 moles. 1.5 • (6.02 X 10^23) gives us the number of molecules in pure O2.
This would be 9.03 X 10 ^23 molecules.
