Question: how many molecules are in one drop?
Answer: Using Avogrado's Number So, next we calculate how many molecules there are in a drop of water, which we determined contains 0.002775 moles: molecules in a drop of water = (6.022 x 1023 molecules/mole) x 0.002275 moles. molecules in a drop of water = 1.67 x 1021 water molecules.