Which of the following is NOT an aerosol?

The correct choice identifies paint thinner as not being an aerosol. Aerosols are generally defined as products that disperse liquid substances into the air in fine droplets, typically through a propellant system within a pressurized can.

Hairspray, Cool Whip, and deodorant all fit the definition of aerosols, as they are packaged in spray cans that utilize propellants to atomize their contents, allowing them to be applied as a mist or spray. In contrast, paint thinner is a liquid solvent used to thin oil-based paints and does not have a pressurized system designed to create an aerosol mist. It is commonly found in liquid form without any propellant mechanism. This fundamental difference in composition and delivery method makes paint thinner the correct answer for the item that is not classified as an aerosol.