Which of the following compounds forms isopropyl cyanide?

Isopropyl cyanide has the structure $\text{CH}_3\text{-CH(CN)-CH}_3$.

To obtain isopropyl cyanide, the starting alkyl halide must contain an isopropyl group, which is $\text{CH}_3\text{-CH(X)-CH}_3$.

When an alkyl halide reacts with alcoholic KCN, the major product is an alkyl cyanide (nitrile). This is because KCN is predominantly ionic, providing free cyanide ions ($\text{CN}^{-}$) in solution. Attack occurs preferentially through the carbon atom as the C-C bond formed is stronger than a C-N bond.

When an alkyl halide reacts with alcoholic AgCN, the major product is an alkyl isocyanide (isonitrile). This is because AgCN is predominantly covalent, leaving the nitrogen atom's lone pair available for nucleophilic attack.

Thus, the reaction of isopropyl bromide ($\text{CH}_3\text{-CHBr-CH}_3$) with alcoholic KCN yields isopropyl cyanide as the major product.

Answer: $\text{CH}_3\text{-CHBr-CH}_3$ and alcoholic KCN