1. Calculate the molarity of a 10.0% (by mass) aqueous solution of hydrochloric acid (density of the solution = 1.05 g/mL).

2. A solution is prepared by dissolving 15.0 g of NH3 in 250.0 g of water. The density of the resulting solution is 0.974 g/mL. The molality of NH3 in the solution is ________ m.

5) The mole fraction of He in a gaseous solution prepared from 1.0 g of He, 6.5 g of Ar, and 10.0 g of Ne is ________.