Here's how to calculate the number of moles of water molecules in a 27 gram sample:

1. Find the molar mass of water (H₂O):

* Hydrogen (H) has a molar mass of approximately 1 g/mol.

* Oxygen (O) has a molar mass of approximately 16 g/mol.

* Molar mass of H₂O = (2 * 1 g/mol) + 16 g/mol = 18 g/mol

2. Use the formula:

* moles = mass / molar mass

3. Plug in the values:

* moles = 27 g / 18 g/mol

* moles = 1.5 mol

Therefore, there are 1.5 moles of water molecules (H₂O) present in a 27 gram sample of water.