Nucleophilic substitution with cyanide to extend carbon chain

Steps:

• Butanoic acid (C3H7CO2H) requires adding one carbon to the propyl chain from 1-iodopropane (C3H7I).
• Primary alkyl iodides undergo SN2 substitution with nucleophiles to replace I.
• CN- from ethanolic KCN acts as nucleophile, forming propanenitrile (C3H7CN).
• Hydrolysis of the nitrile in the second stage yields butanoic acid.

Why C is correct:

• Ethanolic KCN delivers CN- for SN2 reaction, converting C3H7I to C3H7CN per the general formula R-X + KCN → R-CN + KI.

Why the others are wrong:

• A: Aqueous NaOH substitutes to form propan-1-ol (C3H7OH), not extending the chain.
• B: Ethanolic ammonia substitutes to form propan-1-amine (C3H7NH2), yielding an amine.
• D: Ethanolic NaOH favors elimination to propene or substitution to propan-1-ol, not chain extension.

Final answer: C