The value of ${\mathrm{K}}_{\mathrm{f}}$ for water is $1.86°$, calculated from glucose solution. The value of ${\mathrm{K}}_{\mathrm{f}}$ for water calculated for $\mathrm{NaCl}$ solution will be

A solution $\mathrm{M}$ is prepared by mixing ethanol and water. The mole fraction of ethanol in the mixture is $0.9$. 

Given,

$\begin{array}{l}{\mathrm{K}}_{\mathrm{f}} \left(\mathrm{water}\right)=1.86 \mathrm{K} \mathrm{kg} {\mathrm{mol}}^{-1}\\ {\mathrm{K}}_{\mathrm{f}} \left(\mathrm{ethanol}\right)=2.0 \mathrm{K} \mathrm{kg} {\mathrm{mol}}^{-1}\\ {\mathrm{K}}_{\mathrm{b}} \left(\mathrm{water}\right)=0.52 \mathrm{K} \mathrm{kg} {\mathrm{mol}}^{-1}\\ {\mathrm{K}}_{\mathrm{b}} \left(\mathrm{ethanol}\right)=1.2 \mathrm{K} \mathrm{kg} {\mathrm{mol}}^{-1}\end{array}$

Standard freezing point of water $=273 \mathrm{K}$

Standard freezing point of ethanol $=155.7 \mathrm{K}$

Standard boiling point of water $=373 \mathrm{K}$

Standard boiling point of ethanol $=351.5 \mathrm{K}$

Vapour pressure of pure water $=32.8 \mathrm{mmHg}$ 

Vapour pressure of pure ethanol $=40 \mathrm{mmHg}$ 

Molecular weight of water $=18 \mathrm{g} {\mathrm{mol}}^{-1}$

Molecular weight of ethanol $=46 \mathrm{g} {\mathrm{mol}}^{-1}$ 

The freezing point of the solution $\mathrm{M}$ is