(i) The solutions which do not obey Raoult's law over the entire range of concentration are called non-ideal solutions. The deviation of the non-ideal solution from the Raoult's law may be positive (or) negative.
(ii) Example, Ethyl alcohol and cyclohexane.

It is the ratio of the number of moles of a component to the total number of moles of all the components present in a solution.
\(\text { Mole fraction of a components }=\frac{\text { No. of moles of the components }}{\text { Total no. of moles of all the components present in a solution } }\)
\(\mathrm{X}_{\mathrm{A}}=\frac{\mathrm{n}_{\mathrm{A}}}{\mathrm{n}_{\mathrm{A}}+\mathrm{n}_{\mathrm{B}}}\).

It is the ratio nurnber of formula weight of a solute to the volume of the solution in litres.
\(\text { Formality }=\frac{\text {No.of formula weight of the solute }}{\text { Volume of the solution in } \mathrm{L}}\)

Van't Hoff found out that for dilute solutions, the osmotic pressure is directly proportional to the molar concentration ofthe solute and the temperature of the solution. He proposed the following equation to calculate osmotic pressure which is now called as van't Hoff equation.
\(\pi\) = cRT
Here, 
c = Concentration of the solution in molarity
T = Temperature
R = Gas constant

This law states that "in the case of a solution of volatile liquids, the partial vapour pressure of each component (A & B) of the solution is directly proportional to its mole fraction".
According to Raoult's law,
P_A \(\alpha\) X_A
P_A = K X_A
when X_A = 1, K p p⁰
where p⁰ _A is the vapour pressure of pure component 'A' at the same temperature.
Therefore, pA = \({ p }_{ A }^{ 0 }x_{ A }\)

(i) Unlike elevation of boiling point and the depression in freezing point, the magnitude of osmotic pressure is large.
(ii) The osmotic pressure can be measured at room temperature enables to determine the molecular mass ofbiomolecules which are unstable at higher temperature.
(iii) Even for a very dilute solution, the osmotic pressure is large.

Mass of toluene = 40g; Mol mass of toluene = 92
Mass of CHCl₃ = 60g; Mol. mass ofCHCl3 = 119.3
No.of moles of toluene = \(\frac { 40 }{ 92 } \) = 0.4347
No.of. moles of CHCl₃ = \(\frac { 60 }{ 119.3 } \)
= 0.5029
Total moles 0.4347 + 0.5029 = 0.9376
Mole fraction of toluene  =  \(\frac { 0.4347 }{ 0.9376 } \)
0.4636
Mole fraction of CHCl₃  -  \(\frac { 0.5029 }{ 0.9376 } \)
= 0.5363

Unlike elevation of boiling point (for 1 molal solution the elevation in boiling point is 0.512°C for water) and the depression in freezing point (for 1 molal solution the depression in freezing point is . 1.86°C for water), the magnitude of osmotic pressure is large.
The osmotic pressure can be measured at room temperature enables to determine the molecular mass of biomolecules which are unstable at higher temperatures.
Even for a very dilute solution, the osmotic pressure is large

(i) An increase in temperature of the solution increases the average kinetic energy of the molecules present in the solution which causes decrease in the attractive force between them.
(ii) At high pressure the molecules tend to stay close to each other and therefore there will be an increase in their intermolecular attraction.
(iii) When the concentration is increased by adding solute, the solvent-solute interaction becomes significant.

(i) The solubility of a substance at a given temperature is defined as the amount of the solute that can be dissolved in 100 g of the solvent at a given temperature to form a saturated solution.
(ii) Factors influencing solubility
(a) Nature of solute and solvent: Sodium chloride, an ionic compound readily dissolves in polar solvent such as water but it does not dissolve in non polar solvent such as benzene. Most of the organic compounds dissolve in organic solvent and do not dissolve in water.
(b) Effect of temperature: Generally, the solubility of a solid solute in a liquid solvent increases with increase in temperature. The dissolution of NaCI does not vary as the maximum solubility is achieved at normal temperature. The dissolution of ammonium nitrate is endothermic, the solubility increases with increase in temperature. The dissolution of eerie sulphate is exothermic and the solubility decreases with increase of temperature.
In the case of gaseous solute in liquid solvent the solubility decreases with increase in temperature.
Effect of pressure: Generally the change in pressure does not have any significant effect in the solubility of solids and liquids as they are not compressible. However, the solubility of gases generally increases with increase of pressure.

(i) solution is a homogeneous mixture of two or more substances, consisting of atoms, ions or molecules.
(ii) Types and examples of solution.

Mass Percentage of NaCl
= \(\frac { Mass\ of\ NaCl }{ Total\ Mass\ of\ the\ solution } \times 100\)
= \(\frac { 1.75 }{ 1.75+7.88 } =\frac { 1.75 }{ 9.6 } \) = 18.2 %

Let us consider the experimental setup discussed in the osmosis. The pure water moves through the semipermeable membrane to the NaCl solution due to osmosis. is process can be reversed by applying pressure greater than the osmotic pressure to the solution side. Now the pure water moves from the solution side to the solvent side and this process is called reverse osmosis. It can be defined as a process in which a solvent passes through a semipermeable membrane in the .opposite direction of osmosis, when subjected to a hydrostatic pressure greater than the osmotic pressure.
Applications of Reverse osmosis in water purication:
Reverse osmosis is used in the desalination of sea .water and also in the purication of drinking water. A simple set up used in both the process is shown in the figure. When a pressure higher than the osmotic pressure is applied on the solution sided (sea water) the water molecules moves from solution side to the solvent side through semi-permeable membrane (Opposite to the Osmotic flow). The pure water can be collected are different types of semi-permeable membranes used in this process. The membrane used for reverse osmosis has to withstand high pressures. Generally, cellulose acetate or polyamide membranes are commonly used in commercial systems. The selection of membrane used for reverse osmosis will be decided based on the nature of the input water.