Which of the following solutions is isotonic with blood?

$\mathrm{A}$ solution $\mathrm{X}$ contains $12 \mathrm{g}$ of urea per litre of water. Another solution $\mathrm{Y}$ contains $68.4 \mathrm{g}$ of cane sugar per litre of water at the same temperature. The ratio of lowering of vapour pressure in solution $\mathrm{X}$ and $\mathrm{Y}$ is

$\left(\mathrm{N}=14 \mathrm{u}, \mathrm{C}=12 \mathrm{u}, \mathrm{O}=16 \mathrm{u}, \mathrm{H}=1 \mathrm{u}\right)$

An aqueous solution of an unknown solute boils at $373.18 \mathrm{K}$ at the atmospheric pressure. If ${\mathrm{K}}_{\mathrm{f}}$ and ${\mathrm{K}}_{\mathrm{b}}$ for water are $1.86$ and $0.512 \mathrm{kg} {\mathrm{mol}}^{-1}$ respectively, then the freezing point of the solution is

NOTE: Take the boiling point of pure water as $373 \mathrm{K}$