Nucleophilic substitution followed by nitrile hydrolysis

Steps:

• Bromoethane (CH₃CH₂Br) undergoes SN2 reaction with CN⁻ from KCN to form propanenitrile (CH₃CH₂CN).
• Propanenitrile hydrolyzes under acidic conditions with dilute HCl to yield propanoic acid (CH₃CH₂COOH) and NH₄⁺.

Why D is correct:

• KCN supplies CN⁻ for substitution on primary alkyl halide (SN2 favored), and dilute HCl provides H⁺/H₂O for nitrile hydrolysis to carboxylic acid (R-CN + 2H₂O + HCl → R-COOH + NH₄Cl).

Why the others are wrong:

• A: Aqueous NaCN forms nitrile, but acidified K₂Cr₂O₇ oxidizes alcohols, not nitriles directly to acids.
• B: Aqueous NaOH substitutes to ethanol (CH₃CH₂OH), oxidized by K₂Cr₂O₇ to ethanoic acid (2 carbons), not propanoic.
• C: Ethanolic NaOH causes E2 elimination to ethene, oxidized by KMnO₄ to CO₂, not propanoic acid.

Final answer: D