Question: how many molecules of water in a glass?
Answer: A mole is defined as Avogadro's number of particles of any kind of substance (atoms, molecules, or ions). Avogadro's number is approximately 6.022 × 1023. Thus 18.01508 grams of water contain 6.022 × 1023 water molecules. A glass of water, or 200 grams of water, therefore contains 6.6855 × 1024 water molecules.