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 prepare by mixing ethanol and water. The mole fraction of ethanol in the mixture is 0.9

Given :

Freezing point depression constant of water `(K ^(water) _f) = 1.86 K kg mol^(-1)`

Freezing point depression constant of ethanol `(K ^(ethanol) _f) = 2.0 K kg mol^(-1)`

Boiling point elevation constant of water `(K^(water) _b) = 0.52 K kg mol^(-1)`

Boiling point elevation constant of ethanol `(K ^(ethanol) _b) = 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 water = 373 K

Standard boiling point of ethanol = 351.5 K

Vapour pressure pure water = 32.8 mm Hg

Vapour pressure 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.

The freezing point of the solution M is