Paragraph for Question Nos. 67 to 69 Properties such as boiling point, freezing point and vapour pressure of a pure solvent change when solute molecules are added to get homogeneous solution. These are called colligative properties. Applications of colligative properties are very useful in day-to-day life. One of its examples is the use of ethylene glycol and water mixture as anti-freezing liquid in the radiator of automobiles. A solution M is prepared by mixing ethanol and water. The mole fraction of ethanol in the mixture is 0.9. Given : Freezing point depression constant of water (Kfwater) = 1.86 K kg mol–1 Freezing point depression constant of ethanol (Kfethanol) = 2.0 K kg mol–1 Boiling point elevation constant of water (Kbwater) = 0.52 K kg mol–1 Boiling point elevation constant of ethanol (Kbethanol) = 1.2 K kg mol–1 Standard freezing point of water = 273 K Standard freezing point of ethanol = 155.7 K Standard boiling point of ethanol = 373 K Vapour pressure of pure water = 32.8 mm Hg Vapour pressure of pure ethanol = 40 mm Hg Molecular weight of water = 18 g mol–1 Molecular weight of ethanol = 46 g mol–1 In answering the following questions, consider the solutions to be ideal dilute solutions and solutes to be non-volatile and non-dissociative. 1. 67. The freezing point of the solution M is   268.7 K   268.5 K   234.2 K   150.9 K   Hint Half-n-half Clue   2. 68. The vapour pressure of the solution M is   39.3 mm Hg   36.0 mm Hg   29.5 mm Hg   28.8 mm Hg   Half-n-half Clue   3. 69. Water is added to the solution M such that the mole fraction of water in the solution becomes 0.9. The boiling point of this solution is   380.4 K   376.2 K   375.5 K   354.7 K   Half-n-half Clue