The average mass of one mole of H2O is 18.02 grams.
Explanation: we need to find the moles of water in 1 L of water or 1000mL of water. Taking the density of water to be 1g/mL, 1000mL of water= 1000g water.
Therefore, number of moles= given mass of water(1000)/molecular mass of water(18)
Moles =1000/18= 55.55
So total molecules in 55.55 moles= 55.55* 6.022*10^23 = 334.52*10^23 molecules
