How many grams are in 9.45 x 10^23 molecules of H2O?

Avogadro constant = 6.02 × 10²³ /mol
No. of moles of H₂O = (9.45 × 10²³) / (6.02 × 10²³ /mol) = 1.57 mol

Molar mass of H₂O = (1.0×2 + 16.0) g/mol = 18.0 g/mol
Mass of H₂O = (1.57 mol) × (18.0 g/mol) = 28.3 g

One mole consists of avagadro number of molecules. that is 6.022 x 10^23

and one mole of water means 18 gms.

6 x 10^23 molecules -------------------- 18 gms.
9.45 x 10^23 molecules ------------------ ?

thats approx. equal to 28.35 gms.