How many hydrogen atoms are there in a glass of water?

This question may seem extremely broad but in fact there is only one assumption one should make - the volume of the water. Let's say that there are 200mL of water in the glass. We know that the concentration of water under normal conditions is 55.5 M. This is so because one water molecule has a molecular weight of 18 g/mole and the density of water is 1000 g/L. Hence, the concentration of water is 1000 g/L / 18 g/mole = 55.5 MHence in the glass of water there are 55 moles/L x0.2 L = 11 moles of H2O. We also know that the Avogadro number is 6.022x10^23 molecules/mole. Thus there are 6.022 x 10^23 x 11 = 6.6 x 10^24 molecules of H2O in the glass. Because each water molecule contains two hydrogen atoms we need to multiply the previous number by 2 and we get to the final answer - there are 1.3 x 10^25 molecules of hydrogen in the glass. (an interesting fact is that there are ~10^80 hydrogen atoms in the universe)