To solve this problem, we need to analyze the given reaction sequence.$\\$1. The first reaction involves the conversion of a ketone $[A]$ to a cyanohydrin $[B]. \\$ - The reaction is:$\\$ - Cyclohexanone reacts with HCN to form a cyanohydrin.$\\$2. The second step involves the dehydration of the cyanohydrin $[B]$ using conc. $H_2SO_4. \\$ - This step typically leads to the formation of an unsaturated carboxylic acid.$\\$3. The dehydration of the cyanohydrin $[B]$ involves:$\\$ - The hydroxyl group (OH) and the cyano group (CN) form an unsaturated bond.$\\$ - The CN group is converted to a carboxylic acid (COOH) upon hydrolysis.$\\$4. The final product $[C]$ is an unsaturated carboxylic acid.$\\$5. From the options provided, the correct structure for $[C]$ is:$\\$ - Option 4: Cyclohexene carboxylic acid (unsaturated carboxylic acid).$\\$Therefore, the correct answer is Option 4.