Final answer:
The gas evolved during the alkaline hydrolysis of benzonitrile is ammonia.
Step-by-step explanation:
The gas evolved during the alkaline hydrolysis of benzonitrile is ammonia. When benzonitrile undergoes hydrolysis in the presence of an alkaline solution, it is broken down into its constituent parts. The nitrile group (-CN) is hydrolyzed to yield ammonia (NH3) and a carboxylate ion. So, ammonia is the gas that is produced during the alkaline hydrolysis of benzonitrile.