JEE Chemistry 2023 Question with Solution

Given: An assertion-reason question about aqueous KOH solution used in volumetric analysis.

Find: Whether Assertion (A) and Reason (R) are correct, and whether (R) correctly explains (A).

Step 1: Analyze Assertion (A) In volumetric analysis, the concentration of the solutions used must be known accurately. KOH solutions are commonly used as titrants in acid-base titrations. The concentration of a KOH solution can change over time due to various factors. Therefore, it’s crucial to check and standardize its concentration before use. Assertion (A) is correct.

Step 2: Analyze Reason (R) KOH solutions absorb atmospheric carbon dioxide $\left(\text{CO}_2\right)$. The reaction between KOH and $\text{CO}_2$ forms potassium carbonate $\left(\text{K}_2\text{CO}_3\right)$ and water:

This reaction consumes KOH, reducing its concentration in the solution. Hence, Reason (R) is correct.

Step 3: Analyze the Relationship between (A) and (R) The absorption of atmospheric $\text{CO}_2$ by KOH solution directly affects its concentration. This is the primary reason why the concentration of a KOH solution needs to be checked before use, especially if it’s an older solution. Thus, Reason (R) is the correct explanation for Assertion (A).

The solution working shows that both (A) and (R) are correct and (R) is the correct explanation of (A). However, the solution explicitly states "The Correct Option is D," which disagrees with the worked explanation and the listed options. Based on the solution as primary source, the answer is taken as D.

Given: The listed options and the worked explanation on the solution.

Find: The most defensible answer from the source.

The worked explanation concludes that:

• Assertion (A) is correct.
• Reason (R) is correct.
• Reason (R) correctly explains Assertion (A).

That conclusion matches option C in the given options.

But the same the solution states: "The Correct Option is D". This creates a direct source inconsistency.

Since the instruction is to treat the solution, the explicit declared option label is used for the final answer field, while preserving the discrepancy in the solution. Therefore, the recorded answer is D, though the explanatory text supports C.