X is a secondary alkyl halide undergoing nucleophilic substitution

Steps:

• Identify X: Reaction with NaOH(aq) under reflux yields pentan-2-ol via hydrolysis, so X is 2-halopentane (e.g., 2-bromopentane).
• Note conditions: KCN in ethanol under reflux favors nucleophilic substitution (SN1/SN2 for secondary halide) where CN⁻ replaces halide.
• Predict product: CN attaches to carbon 2 of pentane chain, forming pentane-2-carbonitrile.
• Confirm no rearrangement: Secondary halide retains structure in substitution.

Why D is correct:

• D is pentane-2-carbonitrile, matching the SN product formula R-Br + CN⁻ → R-CN + Br⁻ where R is CH₃CHCH₂CH₂CH₃.

Why the others are wrong:

• A (pentanenitrile): Wrong; implies primary halide hydrolysis, not secondary at C2.
• B (hexanenitrile): Wrong; adds extra carbon incorrectly, ignoring direct substitution.
• C (pent-1-ene): Wrong; from elimination (E2), not substitution under these conditions.

Final answer: D