The correct answer is C.
Of the solutions named, solution Y has a higher boiling point than solution
X at the given pressure. Since both solutions are aqueous and contain the
same nonvolatile solute, it follows that solution Y is more concentrated (ΔTb =
Kbm, where m is for molality) and thereby experiences
a more significant boiling point elevation. Vapor pressure is decreased by
increasing solute concentration (PA = XAPtotal,
where XA is the mole fraction of solvent in
the mixture and thus decreases with increasing mole fraction of solute), so the vapor pressure above the
less concentrated solution, solution X, will be greater than that above solution
Y at the same temperature. As for the wrong choices, choice A is incorrect
since freezing point decreases with increasing concentration (ΔTf =
Kfm, where m is for molality), so the more concentrated
solution, solution Y, would be predicted to have a lower freezing point. Choice
B is an unwarranted assumption: solution Y can be more concentrated without
necessarily being saturated. Choice D is false, since 'hypertonic to' means
more concentrated than: solution X is actually hypotonic
to solution Y. Finally, choice E is incorrect since, at the boiling point,
the vapor pressure above either solution will be equal to the atmospheric
pressure. The vapor pressures above the two solutions, at their respective
boiling points, will thus be the same.