Which of the following is not an example of a primary reinforcer?

food

money

water

sex

money

Explanation:

Some reinforcing events in the environment of organisms are characterized by their innate ability to, under the appropriate motivational conditions, strengthen behaviors that produce them (or positive reinforcers) or eliminate them (negative reinforcers). These events, such as food, water, sex, etc., are called primary reinforcing stimuli (or simply, unconditioned or unconditional primary reinforcers).

Money is not considered a primary reinforcer.