How many molecules of water are there in 0.80 Mol of water?

4.816 x 10^23, because the number of atoms in one mole of any compound, mixture, or pure substance is 6.02 x 10^23, and multiplying that by 0.8 moles you get that there are 4.816 x 10^23 atoms in 0.8 moles of water.