Concept:The iodoform test gives a positive result (yellow crystals of \(\text{CHI}_3\)) for compounds containing a methyl ketone group (\(\text{CH}_3\text{CO-}\)) or alcohols that oxidize to methyl ketones (specifically, secondary alcohols with a methyl group on the alpha carbon, or ethanol).
Formula:$$ \text{CH}_3\text{CH}_2\text{OH} + 4\text{I}_2 + 6\text{NaOH} \longrightarrow \text{CHI}_3\downarrow + \text{HCOONa} + 5\text{NaI} + 5\text{H}_2\text{O} $$
Solution:- Among primary alcohols, only ethanol gives a positive iodoform test because it oxidizes to acetaldehyde (which contains the required \(\text{CH}_3\text{CO-}\) group).
Why other options are incorrect:Methanol, 1-butanol, and propanal lack the \(\text{CH}_3\text{CH}(\text{OH})-\) or \(\text{CH}_3\text{CO-}\) structural requirement to form iodoform.
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