Aqueous ammonia is commercially available in a solution that is 28% by mass ammonia. What is the mole fraction of ammonia in such a solution?

0.29

Explanation:

The bottle contain 28 % by mass ammonia and (100 - 28) % remaining water

molar mass of ammonia = 17.031 g/mol

molar mass of water = 18.01528 g/mol

mole of ammonia present = 28 / 17.031 = 1.64 mol

mole of water present = 72 / 18.01528 = 4 mol

mole fraction of ammonia = 1.64 / (4 + 1.64) = 0.29