See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept 1 - Iodoform test (I2/NaOH): A positive iodoform test is given by compounds containing the CH3CO- group (methyl ketones) or CH3CH(OH)- group (secondary alcohols with methyl adjacent to OH), or acetaldehyde (CH3CHO), or ethanol. The key structural requirement is a methyl group directly attached to a carbonyl (CH3C=O) or to a CHOH group. Concept 2 - Extraction by saturated NaHSO3: Saturated sodium bisulfite solution forms addition compounds (bisulfite adducts) with aldehydes, methyl ketones, and cyclic ketones with fewer than 8 carbons. It does NOT react well with ketones where both groups on the carbonyl are large (i.e., dialkyl ketones where neither alkyl is methyl). This test is used to distinguish reactive carbonyl compounds from unreactive ones. Now evaluate each option: (a) CH3(CH2)4CHO - This is hexanal (an aldehyde). It would give a positive NaHSO3 test (aldehydes react). However, for iodoform test, the aldehyde must be CH3CHO specifically, or have CH3CO-. Hexanal does NOT have a CH3CO- group (it has a -CHO at the end of a long chain with no adjacent methyl to carbonyl in the CH3CO sense). So hexanal fails the iodoform test. Eliminated. (b) CH3(CH2)3COCH3 - This is 2-hexanone (methyl n-butyl ketone). It has the CH3CO- group, so it GIVES a positive iodoform test. It is a methyl ketone, so it also reacts with saturated NaHSO3 to form a bisulfite adduct, meaning it can be extracted from benzene by NaHSO3. Both conditions are satisfied. (c) CH3CH2COCH2CH3 - This is 3-pentanone (diethyl ketone). It does NOT have a CH3CO- group (both sides of the carbonyl are ethyl groups), so it FAILS the iodoform test. Also, diethyl ketone is a symmetric dialkyl ketone and does not react well with NaHSO3 (borderline, but primarily it fails iodoform). Eliminated. (d) CH3(CH2)4CH2OH - This is 1-hexanol (a primary alcohol). Primary alcohols do not give a positive iodoform test (only CH3CH(OH)- secondary alcohols or CH3CH2OH give it). Also, primary alcohols are not extracted by NaHSO3. Eliminated. Only option (b) CH3(CH2)3COCH3 satisfies both conditions: positive iodoform test (methyl ketone, CH3CO- group present) and extraction by saturated NaHSO3 (methyl ketones form bisulfite adducts). Therefore, the correct answer is B.