Iodoform test identifies methyl ketones and oxidizable alcohols in hydroxy carbonyls

Steps:

• Molecular formula C3H6O2 accommodates structural isomers with one carbonyl (aldehyde or ketone) and one OH group.
• The isomers are 3-hydroxypropanal (HOCH₂CH₂CHO), 2-hydroxypropanal (CH₃CH(OH)CHO), and 1-hydroxypropan-2-one (CH₃COCH₂OH).
• 1-Hydroxypropan-2-one contains CH₃CO- group, undergoes triiodination and cleavage to CHI₃ at room temperature.
• 2-Hydroxypropanal's secondary OH oxidizes to CH₃COCHO (methylglyoxal), a methyl ketone equivalent that gives CHI₃; 3-hydroxypropanal's primary OH oxidizes to OHCCH₂CHO (malonaldehyde), whose active CH₂ enables analogous reaction to CHI₃.

Why B is correct:

• Exactly three isomers exist, and all react positively per haloform mechanism to form yellow CHI₃ crystals.

Why the others are wrong:

• A: Misses that all three isomers qualify under iodoform conditions.
• C: Exceeds the three valid structural isomers.
• D: Exceeds the three valid structural isomers.

Final answer: B