Heating with Br2 and KOH reduces any carbonyl group so we can us that as a hint to obtain the starting product. As the formula C6H7N suggests the starting product is benzene with carbonyl group attached to it. We can guess it to be benzamide as it contains a nitrogen atom, and when it is reduced with Br2 it reduces to aniline or benzamine.
Aniline when treated with chloroform in presence of KOH it forms isocyanide which gives off the fouling smell.
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