Question: how many molecules are there in the water?
Answer: Avogadro's number tells us that there are 6.022 x 10^23 molecules of water per mole of water. So, next, we calculate how many molecules there are in a drop of water, which we determined: molecules in a water drop = (6.022 x 102^3 molecules/mole) x 0.002275 moles.