Cyanides Versus Isocyanides

The cyanide ion is an ambident nucleophile, meaning it can attack an electrophilic carbon through either its carbon atom or its nitrogen atom, and the metal counter-ion controls which end reacts. Potassium cyanide is largely ionic, so the free cyanide attacks predominantly through its more nucleophilic carbon, giving an alkyl nitrile R–C≡N. Silver cyanide is largely covalent, so the carbon end is less available and the nitrogen lone pair attacks instead, producing an alkyl isocyanide R–N≡C. Hence the two reagents give constitutional isomers differing in the atom bonded to the alkyl group. The option that both give the same nitrile ignores the ambident behaviour and the role of the metal, so it is wrong. The reversed assignment is incorrect because it contradicts the ionic-versus-covalent argument. Neither reagent gives a carboxylic acid directly; that requires subsequent hydrolysis of the nitrile. This ambident nucleophile behaviour is a standard NCERT and JEE Main concept that also explains why hydrolysis of the two products diverges, since nitriles give carboxylic acids while isocyanides give amines. As a plausibility check, the nitrile and isocyanide have the same molecular formula but different connectivity, confirming they are constitutional isomers selected purely by the ionic or covalent character of the chosen metal cyanide.