The number of molecules in 18 mg of water in terms of Avogadro number NA is (J&K CET 2009)

1 mole of water ( 2 H O ) contains Avogadro number of molecules That means, 18 grams ( 2+16 ) of water contains Avogadro number of molecules Given, Mass of water = 18 mg = 3 18 10 g x Mass of water Molecules of water (grams) ( 23 6.022 10 A N x ) 18 A N 3 18 10 g x X Solving for x, we get 3 3 18 10 10 18 A A N N x x Therefore, 18 mg of water contains the 3 1 0 A N number of molecules.