3.342 x 10^24 molecules of water
Given;
Mass of water = 100.0 g
Required to determine the number of molecules in 100.0 g of water
Using Avogadro's constant
1 mole of a compound contains 6.022 × 10^22 molecules
Thus;
1 mole of H₂O contains 6.022 × 10^23 molecules
But;
1 mole = 18.02 g/mol
Therefore;
18.02 g of water contains 6.022 × 10^23 molecules
100.0 g of water will have;
= (100. 0 g ×6.022 × 10^23 molecules) ÷ 18.02
= 3.342 x 10^24 molecules