The correct option is C 5.18×1023
The molecular formula of water is H2O.
Molecular mass of water = 2 + 16 = 18 u.
So, gram molecular mass of water = 18g
Thus, 1 mole of water has a mass of 18 g and it contains 6.023×1023 molecules of water.
So, 15.5 g of water contains =(6.023×102318)×15.5