Explanation

[Solution from source] 1.00 molal means 1 mol solute per 1000 g water, i.e. 1000/18 = 55.56 mol water. Mole fraction of solute = 1/(1 + 55.56) = 0.0177. Note this is the mole fraction, not the molality, so it must be much smaller than 1; 0.177 is a decimal slip. Answer (3).