Which of the following compounds will give a positive iodoform test?

Solution

1. The iodoform test is given by compounds containing the ${\text{CH}}_3\text{CO}-$ group or the ${\text{CH}}_3\text{CH(OH)}-$ group.
2. 3-pentanone lacks the ${\text{CH}}_3\text{CO}-$ moiety.
3. 2-pentanone contains the ${\text{CH}}_3\text{CO}-$ group attached to a propyl chain.
4. Benzaldehyde does not contain a methyl ketone group.
5. Hence the answer is (B).