What is the composition of the vapor in an ideal solution represented by y_A?

In the context of an ideal solution, the vapor phase composition can be related to the liquid phase composition through Raoult’s law. In an ideal solution, the partial vapor pressure of each component is directly proportional to its mole fraction in the liquid phase and its pure component vapor pressure.

The correct expression reflects the relationship between the mole fraction of component A in the vapor phase (y_A) and the mole fraction of component A in the liquid phase (x_A). According to Raoult's law, the partial pressure of component A in the vapor phase is given by p*_A * x_A, where p*_A represents the pure component vapor pressure of A.

The total pressure of the system is the sum of the contributions from both components, so the total pressure can be expressed as the sum of the vapor pressures of each component. For component A, the vapor composition is determined by the ratio of its contribution to the total vapor pressure.

The formula y_A = x_A * p*_A / (p*_A + (p*_B − p*_A) * x_A) encapsulates this relationship effectively. Here, (p*_B − p*_A) * x_A represents the contribution of component B to the total pressure