How many molecules are im 4.9 moles of h2o?

The number of units in one mole of a substance is 6.022140857 * 10^23. This is irregardless of whether the particle is an atom, a molecule or an ion.

Therefore, we multiply the number of moles by the Avogadro's number

4.9*6.022140857 * 10^23 = 2.95084902*10^24 molecules