A binary solution of two volatile liquids and denote the two components as 1 and 2. When taken in a closed vessel, both the components would evaporate and eventually an equilibrium would be established between vapour phase and the liquid phase. Let the total vapour pressure at this stage be p_total and p₁ and p₂ be the partial vapour pressures of the two components 1 and 2 respectively. These partial pressures are related to the mole fractions x₁ and x₂ of the two components 1 and 2 respectively. The French chemist, Francois Marte Raoult (1886) gave the quantitative relationship between them. The relationship is known as the Raoult’s law which states that for a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution.

Which of the following is correct about a solution showing positive deviation from Raoult's law?

Both (1) and (3)

Raoult's law is a principle that describes the behavior of ideal solutions. According to Raoult's law, the partial vapor pressure of each component in an ideal solution is directly proportional to its mole fraction in the solution and the vapor pressure of the pure component. Mathematically, for component i, Raoult's law can be expressed as:
\[ P_i = x_i \cdot P_{i, \text{pure}} \]
where:
\( P_i \) is the partial vapor pressure of component i in the solution,
\( x_i \) is the mole fraction of component i in the solution,
\( P_{i, \text{pure}} \) is the vapor pressure of pure component i.

A solution that deviates from Raoult's law can exhibit either positive or negative deviation.

1. Positive Deviation from Raoult's Law:
Enthalpy of Mixing (\( \Delta H_{\text{mix}} > 0 \)): In a solution with positive deviation, the interactions between unlike molecules are weaker than those predicted by Raoult's law. As a result, energy is required to break these weaker interactions and mix the components. The positive value of \( \Delta H_{\text{mix}} \) indicates an endothermic process.

Volume of Mixing (\( \Delta V_{\text{mix}} > 0 \)): The volume occupied by the mixture is greater than the sum of the individual volumes of the pure components. This increase in volume can be attributed to the fact that the molecules do not pack as closely as expected due to weaker interactions.

In summary, positive deviation occurs when the interactions between unlike molecules are weaker than expected, leading to a higher observed vapor pressure and an increase in volume upon mixing.

Therefore, in the context of the options provided:

Option 1 (\( \Delta H_{\text{mix}} > 0 \)): This is correct. Positive deviation is associated with an endothermic process, and \( \Delta H_{\text{mix}} \) is indeed greater than 0.

Option 3 (\( \Delta V_{\text{mix}} > 0 \)): This is also correct. Positive deviation is associated with an increase in volume upon mixing, so \( \Delta V_{\text{mix}} \) is greater than 0.

Hence, the correct answer is Option 4: Both (1) and (3).