Assertion : When one solvent mixed with other solvent, vapour pressure of one increases an decreases.
Reason : When any solute added into solvent, vapour pressure of solvent decreases

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both asertion and reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
**Assertion**: When one solvent is mixed with another solvent, the vapor pressure of one increases and that of the other decreases.

- When two solvents are mixed, the vapor pressure of each solvent can change depending on their interactions. If the solvents are similar, the vapor pressure of one may increase while the other decreases due to changes in mole fraction and intermolecular forces. This statement is true.

### Step 2: Analyze the Reason
**Reason**: When any solute is added to a solvent, the vapor pressure of the solvent decreases.

- This statement is also true. According to Raoult's Law, the addition of a solute to a solvent lowers the vapor pressure of the solvent because the solute particles occupy space at the surface, reducing the number of solvent molecules that can escape into the vapor phase.

### Step 3: Determine the Relationship Between Assertion and Reason
- Both the assertion and the reason are true, but the reason does not explain the assertion. The assertion discusses the mixing of two solvents, while the reason pertains to the effect of adding a solute to a solvent.

### Conclusion
- Therefore, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

### Final Answer
The correct option is **B**: Assertion and reason are true, but reason is not the correct explanation of assertion.

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