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

Step 1: State the assertion to be judged.
Assertion A says that for an ideal solution of P and Q, \(\Delta_{mix}H = 0\) and \(\Delta_{mix}V = 0\).
Step 2: Check the assertion.
An ideal solution obeys Raoult's law over the whole composition range, and a standard property is exactly that the enthalpy and volume of mixing are both zero. So Assertion A is correct.
Step 3: State the reason.
Reason R claims that no interactions occur between P and Q.
Step 4: Check the reason carefully.
Interactions certainly do exist between P and Q. What makes the solution ideal is that the P-Q interactions are nearly equal in strength to the P-P and Q-Q interactions, written \(P-P \approx Q-Q \approx P-Q\), not that they are absent.
Step 5: Explain why "no interactions" is wrong.
If there were truly no P-Q interactions, the energy of broken P-P and Q-Q contacts would not be compensated and the solution would not behave ideally. So the reason is incorrect.
Step 6: Conclude.
Assertion correct, Reason incorrect. This is the option "A is correct but R is not correct."
\[ \boxed{\text{A is correct but R is not correct.}} \]