The vapour pressure vs. temperature curve for a solution solvent system is shown below.

The boiling point of the solvent is __________ $${ }^{\circ} \mathrm{C}$$.

Consider the following pairs of solution which will be isotonic at the same temperature. The number of pairs of solutions is / are ___________.

A. $$1 ~\mathrm{M}$$ aq. $$\mathrm{NaCl}$$ and $$2 ~\mathrm{M}$$ aq. urea

B. $$1 ~\mathrm{M}$$ aq. $$\mathrm{CaCl}_{2}$$ and $$1.5 ~\mathrm{M}$$ aq. $$\mathrm{KCl}$$

C. $$1.5 ~\mathrm{M}$$ aq. $$\mathrm{AlCl}_{3}$$ and $$2 ~\mathrm{M}$$ aq. $$\mathrm{Na}_{2} \mathrm{SO}_{4}$$

D. $$2.5 ~\mathrm{M}$$ aq. $$\mathrm{KCl}$$ and $$1 ~\mathrm{M}$$ aq. $$\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}$$

Mass of Urea $$\left(\mathrm{NH}_{2} \mathrm{CONH}_{2}\right)$$ required to be dissolved in $$1000 \mathrm{~g}$$ of water in order to reduce the vapour pressure of water by $$25 \%$$ is _________ g. (Nearest integer)

Given: Molar mass of N, C, O and H are $$14,12,16$$ and $$1 \mathrm{~g} \mathrm{~mol}^{-1}$$ respectively

$$20 \%$$ of acetic acid is dissociated when its $$5 \mathrm{~g}$$ is added to $$500 \mathrm{~mL}$$ of water. The depression in freezing point of such water is _________ $$\times 10^{-3}{ }^{\circ} \mathrm{C}$$.

Atomic mass of $$\mathrm{C}, \mathrm{H}$$ and $$\mathrm{O}$$ are 12,1 and 16 a.m.u. respectively.

[Given : Molal depression constant and density of water are $$1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$ and $$1 \mathrm{~g} \mathrm{~cm}^{-3}$$ respectively.]