The first step in calculating the number of molecules in 3 g of water is to identify the molar masses of H and O.
This step is essential because you need the molar mass of water in order to calculate the number of moles from the mass provided. Once the molar masses of hydrogen (H) and oxygen (O) are known, you can then determine the molar mass of water (H₂O) and subsequently calculate the number of moles before applying Avogadro's number.