Assertion A: For an ideal solution formed by mixing liquids P and Q, Δ_mixH=0 and Δ_mixV=0. Reason R: No interactions occur between P and Q. Choose the most appropriate answer:

Solution & Explanation

Concept — Definition and molecular basis of an ideal solution (Raoult's-law solution). Assertion A: For an ideal solution, Δ_mixH = 0 (no heat absorbed or released on mixing) and Δ_mixV = 0 (volumes are additive, no contraction or expansion). This is the defining thermodynamic behaviour of an ideal solution → A is CORRECT. Reason R: "No interactions occur between P and Q" is FALSE. Intermolecular interactions certainly DO occur between P and Q molecules in solution. The actual condition for ideality is that the P–Q interactions are essentially equal in magnitude to the average of the P–P and Q–Q interactions present in the pure liquids. Because the new P–Q interactions just replace equally strong P–P/Q–Q interactions, there is no net energy or volume change — but that is similarity of interactions, not their absence. So A is correct while R is an incorrect statement. Hence the answer is: A is correct but R is not correct — option C.