(a) (i) Define osmotic pressure. Why is it considered as a colligative property ? (ii) The vapour pressure of two pure liquids A and B at $400\text{ K}$ are $450$ and $700\text{ mmHg}$ respectively. Find out the composition of liquid mixture if the total vapour pressure of mixture is $600\text{ mmHg}$. OR (b) (i) What type of deviation from Raoult's law is expected when phenol and aniline are mixed with each other ? What change in the net volume of the mixture and enthalpy is expected ? (ii) Boiling point of water at $750\text{ mmHg}$ is $99\cdot48^{\circ}\text{C}$. How much sucrose ($\text{M} = 342\text{ g mol}^{-1}$) is to be added to $500\text{ g}$ of water such that it boils at $100^{\circ}\text{C}$ ? [$K_b$ for water $= 0\cdot52\text{ K kg mol}^{-1}$]