5 moles of water contains 5 moles of H2, therefore contains 10 moles of H atoms. The number of atoms in one mole of a substance is given by avogadros constant, which is 6.02*10^23. Thus the number of hydrogen atoms in 5 moles of water = 10 * (6.02*10^23) = 6.02*10^24 H atoms.