Nucleophilic substitution with cyanide ion

Steps:

• Identify X as an alkyl halide (e.g., R-Br), which undergoes SN reaction.
• KCN in ethanol provides CN⁻ nucleophile; ethanol is polar protic solvent favoring SN1/SN2.
• Heating under reflux promotes substitution, replacing halide with CN.
• Product is alkyl nitrile (R-CN), as CN⁻ attacks carbon, displacing leaving group.

Why D is correct:

• D shows the nitrile (R-CN), formed via SN mechanism where CN⁻ bonds to alkyl chain per nucleophilic substitution definition.

Why the others are wrong:

• A is alkene from E2 elimination, requiring strong base, not CN⁻.
• B is ether from solvolysis, but CN⁻ competes and dominates.
• C is alcohol from hydrolysis, needing water, not ethanol alone.

Final answer: D