0.05 mole of a non-volatile solute is dissolved in 500 g of water. What is the depression in freezing point of resultant solution?

$$\left(K_f\left(\mathrm{H}_2 \mathrm{O}\right)=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$$

Which of the following form an ideal solution?

I. Chloroethane and bromoethane

II. Benzene and toluene

III. $$n$$-hexane and $$n$$-heptane

IV. Phenol and aniline

A solution containing 6.0 g of urea is isotonic with a solution containing 10 g of a non-electrolytic solute $$X$$. The molar mass of X (in g $$\mathrm{mol}^{-1}$$) is

$$x \%(w / V)$$ solution of urea is isotonic with $$4 \%$$ $$(w / V)$$ solution of a non-volatile solute of molar mass $$120 \mathrm{~g} \mathrm{~mol}^{-1}$$. The value of $$x$$ is