See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Step 1: Identify product (A). Acetylene (H-C≡C-H) undergoes acid-catalyzed hydration in the presence of HgSO4 and H2SO4. By Markovnikov's rule, water adds across the triple bond to give an enol which tautomerizes to the more stable carbonyl compound. Since acetylene is symmetric, the product is acetaldehyde (CH3CHO). So (A) = CH3CHO. Step 2: Identify product (B). Acetaldehyde undergoes the Strecker synthesis: treatment with NH3 and HCN gives an alpha-aminonitrile intermediate. NH3 and HCN add across the carbonyl of CH3CHO: NH3 first forms a hemiaminal/imine (aldimine), then HCN adds to give CH3-CH(NH2)-CN (alpha-aminopropionitrile). Subsequent acid hydrolysis (H3O+) of the nitrile group converts -CN to -COOH, yielding CH3-CH(NH2)-COOH, which is 2-aminopropanoic acid = Alanine. Step 3: Why other options fail: - Glycine (H2N-CH2-COOH) would require formaldehyde (HCHO) as starting aldehyde, which would come from a one-carbon alkyne — not applicable here. - Valine has an isopropyl side chain, requiring a branched aldehyde precursor. - Leucine has an isobutyl side chain, requiring a longer aldehyde precursor. Only Alanine matches the two-carbon chain (methyl group) from acetaldehyde via Strecker synthesis. Therefore, the correct answer is B.