Question: how many molecules of water are present in a drop of water which has a mass of 50g?
Answer: So number of moles of water in 50 mg or 0.05 g of water is equal to (1/18) * 0.05 i.e, 2.78 * 10^-3 mol. (2.78 * 10^-3) * (6.022 * 10^23) = 1.67 * 10^21 numbers of water molecule.