Final answer:
The sodium chloride solution will have the lowest water vapor pressure because it dissociates into two particles, which lowers the water's vapor pressure due to the impeding effect of nonvolatile solutes on solvent evaporation.
Step-by-step explanation:
The student's question is asking which aqueous solution among the options provided will have the lowest water vapor pressure. According to the principles of collative properties, the addition of a solute to a solvent decreases the solvent's vapor pressure. This effect is known as Raoult's law, where the vapor pressure of a solution is directly proportional to the mole fraction of the solvent. The aqueous solutions listed—sodium chloride solution, ethanol solution, and sugar solution—all contain solutes that are expected to lower the vapor pressure of water due to the presence of nonvolatile solutes that impede the evaporation of solvent molecules. Out of the solutions provided, sodium chloride (NaCl) will produce the most significant effect because it dissociates into two particles: Na+ and Cl-. This ionization effectively doubles the number of particles in solution compared to non-electrolyte solutes like sugar and thus exerts the highest osmotic pressure, causing the lowest vapor pressure. Therefore, the sodium chloride solution will have the lowest water vapor pressure.