The phase diagram given below shows the relationship between vapor pressure and temperature for pure ethanol and for a solution of ethanol containing a nonvolatile solute.
Use this diagram to determine the approximate molality of the solute in solution. (K_b for ethanol is 1.2 °C/m)

• A. 3.53 mol/kg
• B. 4.74 mol/kg
• C. 4.17 mol/kg
• D. 3.88 mol/kg

Answer: (C)