Question: how many molecules are present in 16g of oxygen gas?
Answer: The number of molecules in 16 gm of oxygen are 0.5 (= 16/32 moles). Thus the number of molecules in 16 gm or 0.5 mole of oxygen gas are 0.5 x 6.023 x 10^(23) = 3.012 x 10^(23) molecules.