JEE Chemistry 2026 Question with Solution

Given: Iodoform test is to be used to check which pairs can be differentiated.

Find: Which listed pair(s) give different iodoform test results.

Iodoform test distinguishes compounds containing $CH_3CO-$ or $CH_3CH(OH)-$ group.

• A. Ethanol gives a positive test, while methanol gives a negative test. So this pair is differentiated.
• B. $CH_3COOH$ and $CH_3CH_2COOH$ are both carboxylic acids, and neither gives a positive iodoform test. So this pair is not differentiated.
• C. Cyclohexene and cyclohexanone are both negative. Cyclohexanone is not a methyl ketone. So this pair is not differentiated.
• D. Diethyl ether is negative. Pentan-$3$-one $\left(CH_3CH_2COCH_2CH_3\right)$ is also negative. So this pair is not differentiated.
• E. Acetone $\left(CH_3COCH_3\right)$ gives a positive test, while anisole gives a negative test. So this pair is differentiated.

Therefore, the test differentiates pairs A and E only.

Hence, the correct option is C.

Given: If both or neither compound gives a positive result, the test fails to differentiate them.

Find: Which option matches the differentiable pairs.

Check each pair by the iodoform test criterion:

1. Compounds with $CH_3CO-$ or $CH_3CH(OH)-$ respond positively.
2. If one is positive and the other is negative, the pair is differentiated.
3. If both are positive or both are negative, the pair is not differentiated.

Applying this:

• A: Methanol and ethanol $\rightarrow$ only ethanol responds positively.
• B: $CH_3COOH$ and $CH_3CH_2COOH$ $\rightarrow$ both negative.
• C: Cyclohexene and cyclohexanone $\rightarrow$ both negative.
• D: Diethyl ether and pentan-$3$-one $\rightarrow$ both negative.
• E: Anisole and acetone $\rightarrow$ only acetone is positive.

Thus only A and E are differentiated, which matches option C.