JEE Main 2025 Apr 3 Shift 1, Chemistry Q11: Properties and Important Reactions of Aldehydes & Ketones

The iodoform test is positive for compounds containing either a ${\text{CH}}_3\text{-CO-}$ group or a ${\text{CH}}_3\text{-CH(OH)-}$ group (which is oxidised to the methyl ketone in situ).

Screening each molecule:

✓ Ethanol (${\text{CH}}_3{\text{CH}}_2\text{OH}$), Isopropyl alcohol, Bromoacetone, 2-Butanol, 2-Butanone, 2-Pentanone — all carry the required ${\text{CH}}_3\text{CO-}$ or ${\text{CH}}_3\text{CH(OH)-}$ moiety.

✗ Compounds without the required group: Butanal, 3-Pentanone, Pentanal, 3-Pentanol. The aldehydes here are not acetaldehyde (no ${\text{CH}}_3\text{CHO}$), and 3-pentanone and 3-pentanol have ethyl groups flanking the C=O/C–OH, not methyl.

Hence 4 molecules do not give iodoform.