Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion…
Redox Reactions · Class 11 · JEE Main Previous Year Question
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): An aqueous solution of KOH when used for volumetric analysis, its concentration should be checked before the use. Reason (R): On aging, KOH solution absorbs atmospheric .
In the light of the above statements, choose the correct answer from the options given below.
- a
(A) is not correct but (R) is correct
- b
Both (A) and (R) are correct but (R) is not the correct explanation of (A)
- c✓
Both (A) and (R) are correct and (R) is the correct explanation of (A)
- d
(A) is correct but (R) is not correct
Both (A) and (R) are correct and (R) is the correct explanation of (A)
Step 1 — Evaluate Assertion (A):
KOH solution is used as a standard base in volumetric analysis. However, KOH is not a primary standard because:
- It absorbs from air:
- This changes the effective concentration of KOH over time
Therefore, its concentration must be checked (standardised) before use. Assertion (A) is CORRECT ✓
Step 2 — Evaluate Reason (R):
KOH solution does indeed absorb atmospheric on aging, converting KOH to . This reduces the KOH concentration and introduces , which has different neutralisation behaviour. Reason (R) is CORRECT ✓
Step 3 — Is R the correct explanation of A?
Yes — the reason KOH concentration must be checked is precisely because it absorbs and its concentration changes. R directly explains A.
Answer: Option (3) — Both correct, R is the correct explanation of A
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