200 g of $20 \% \frac{\mathrm{w}}{\mathrm{w}}$ urea solution is mixed with 400 g of $40 \% \frac{w}{w}$ urea solution. What is the weight percentage $\left(\frac{w}{w} \%\right)$ of resultant solution?

At 293 K , methane gas was passed into 1 L . of water. The partial pressure of methane is 1 bar. The number of moles of methane dissolved in 1 L water is ( $K_{\mathrm{H}}$ of methane $=0.4 \mathrm{~K}$ bar)

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