Concept:The given reaction is benzoin condensation, where two aldehyde molecules combine to form an α-hydroxy ketone.
Explanation:Benzaldehyde (
C6H5CHO) reacts with alcoholic KCN to produce benzoin.
The product formed has two benzene rings and a
−CH(OH)CO− linkage.
This characteristic product is obtained only from benzaldehyde among the given options.
Formaldehyde and acetaldehyde do not give this condensation product.
Acetic acid is not an aldehyde, so it cannot undergo this reaction.
Hence, reactant A is benzaldehyde.
Answer:Option C:
C6H5CHO (benzaldehyde).
