How many molecules are in 128g of H2O?

4.28x10^24 molecules

Explanation:

From Avogadro's hypothesis, 1mole of any substance contains 6.02x10^23 molecules. From the above, we understood that 1mole of H2O also contains 6.02x10^23 molecules.

1mole of H2O = (2x1) + 16 = 2 + 16 = 18g

Now, if 18g of H2O contains 6.02x10^23 molecules,

Then 128g of H2O will contain = (128x 6.02x10^23) / 18 = 4.28x10^24 molecules