Answer:
Option A = pure water
Explanation:
The pure water will have the lowest boiling point as compared to the other given solution.
Reason:
The pure water is just the solvent while other given options are solution which means that solute is present in it. The vapor pressure of the solvent goes to decrease when solute is added. Thus boiling point is increases because more heat is needed in order to create the vapor pressure equal to the external pressure.
The boiling points of solvents thus changes above the solution as the concentration of solute varies. In given solutions the 2.0 m NaCl will have highest boiling point because of high concentration of sodium chloride while 0.5 m NaCl will have lowest boiling point after the pure water.
Mathematical expression:
ΔT = Kbm
ΔT = change in the boiling point
Kb = Boiling point elevation constant
m = molal concentration of solute
The change in the boiling point of solvent above solution will directly proportional to the solute concentration.
