Q.Write the structures and IUPAC names of the two possible products when bromoethane reacts with $(a)$ $\text{KCN}$ and $(b)$ $\text{AgCN}$, and state which is the alkyl cyanide and which is the alkyl isocyanide.

Both reactions start from the same bromoethane and the same $\text{CN}^-$ ambident nucleophile, but differ in which metal supplies it. $(a)$ With ionic $\text{KCN}$, the harder carbon end of cyanide attacks, giving the alkyl cyanide (nitrile): $\text{CH}_3\text{CH}_2\text{Br} + \text{KCN} \to \text{CH}_3\text{CH}_2\text{CN} + \text{KBr}$, named propanenitrile (or ethyl cyanide). $(b)$ With covalent $\text{AgCN}$, the softer nitrogen end attacks instead, giving the alkyl isocyanide: $\text{CH}_3\text{CH}_2\text{Br} …

Identify $\text{CN}^-$ as ambident, then match each metal salt to the end of …

Swapping the two products -- assuming $\text{KCN}$ gives the isocyanide and $\text{AgCN}$ gives th …