Question

Assertion A : For an ideal solution formed by mixing liquids P and Q, \(\Delta_{mix}H=0\) and \(\Delta_{mix}V=0\). Reason R : No interactions occur between P and Q. In the light of the above statements, choose the most appropriate answer from the options given below.

• A. A is not correct but R is correct.
• B. Both A and R are correct and R is the correct explanation of A.
• C. Both A and R are correct but R is NOT the correct explanation of A.
• D. A is correct but R is not correct.

Hint:

For an ideal solution: \[ P-P \approx P-Q \approx Q-Q \] Remember: intermolecular forces are not absent; they are approximately equal. This is why \[ \Delta H_{mix}=0 \quad \text{and} \quad \Delta V_{mix}=0. \]

Answer 1

The Correct Option is D

Concept: An ideal solution is a solution that obeys Raoult's law over the entire range of composition. For an ideal solution: \[ \Delta H_{mix}=0 \] and \[ \Delta V_{mix}=0 \] This happens because the intermolecular forces between unlike molecules are nearly equal to those between like molecules.

Step 1: Examine Assertion A. Assertion states: \[ \Delta H_{mix}=0 \] and \[ \Delta V_{mix}=0 \] for an ideal solution. This is a standard property of ideal solutions. Therefore Assertion A is correct.

Step 2: Examine Reason R. Reason states: No interactions occur between P and Q This statement is incorrect. In reality, interactions do exist between P and Q molecules. For an ideal solution, \[ P-P \approx Q-Q \approx P-Q \] The intermolecular attractions are not absent; they are simply nearly equal in magnitude.

Step 3: Why is the reason incorrect? If there were truly no interactions between P and Q molecules, the solution would not exhibit ideal behaviour. Ideal behaviour requires that the newly formed \(P-Q\) interactions compensate exactly for the broken \(P-P\) and \(Q-Q\) interactions. Thus, Interactions exist, but they are comparable in strength.

Step 4: Final conclusion. Assertion A is correct. Reason R is incorrect. Therefore, \[ \boxed{\text{Option (D)}} \]