(a) (i) Molarity of a solution is defined as the number of moles of solute present in one litre of the solution.
(ii) Molal elevation constant $\left({\mathrm{K}}_{\mathit{b}}\right)$ is defined as the elevation of the boiling point of a solution when one mole of a non-volatile solute is dissolved in one kilogram of a volatile solvent.
(b) Given; Mass of urea, ${\mathrm{W}}_{\mathrm{B}}=15\mathrm{g}$
Molar mass of urea,
The solution of urea in water is isotonic to that of glucose solution.






OR
(a) According to Raoult's law, the partial pressure of a component is the product of vapour pressure of pure solvent and mole fraction of that component. When a solution shows deviation from Raoult's law over the complete range of concentration, the solution is known as a non-ideal solution.
The vapour pressure of the non-ideal solution can be higher or lower than the vapour pressure predicted by Raoult's law.
If the vapour pressure of the non-ideal solution is higher than the vapour pressure predicted by Raoult's law, the deviation is known as positive deviation.
If the vapour pressure of the non-ideal solution is lower than the vapour pressure predicted by Raoult's law, the deviation is known as negative deviation.
The reason for the deviation is molecular interactions, for positive deviation
Here, A is the solute and B is the solvent so, A-B shows the interaction between solute and solvent.
(b) The number of moles of glucose
$=\frac{10}{180}=0.056\mathrm{mol}$
$=\frac{0.056\mathrm{mol}}{0.09\mathrm{kg}}=0.62\mathrm{m}$
If the density of the solution is $1.2{\mathrm{gmL}}^{-1}$, then the volume of the $100\mathrm{g}$ solution can be given as,
$\frac{100\mathrm{g}}{1.2{\mathrm{mL}}^{-1}}=83.3\mathrm{mL}$
$=83.33\times {10}^{-3}\mathrm{L}$
$=\frac{0.056\mathrm{mol}}{83.33\times {10}^{-3}\mathrm{L}}=0.67\mathrm{M}$