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

the answer is b & c i believe : )