Chemistry - Liquid Solution Question with Solution | TestHub

When a non-volatile solute is added to a volatile solvent, the vapor pressure of the solution decreases because a fraction of the surface area is occupied by non-volatile solute particles, reducing the escaping tendency of solvent molecules.

Let $P_1$ be the vapor pressure of the solvent in the solution and $P_1^0$ be the vapor pressure of the pure solvent. According to Raoult's law, the vapor pressure of the solution is directly proportional to the mole fraction of the solvent ($X_1$).

$P_1=P_1^0{X}_1$

Since the mole fraction of the solvent in a solution is always less than 1 ($X_1<1$), it follows that $P_1<P_1^0$.

Due to the lowering of vapor pressure, the solution must be heated to a higher temperature to make its vapor pressure equal to the external pressure, resulting in an elevation in boiling point ($T_b>T_b^0$).

Similarly, the freezing point of the solution is lower than that of the pure solvent, resulting in freezing point depression ($T_f<T_f^0$).

Thus, the only correctly represented relationship among the given options is $P_1<P_1^0$.

Answer: $P_1<P_1^0$