Which of the following is NOT considered a primary reinforcer?

A primary reinforcer is a stimulus that is naturally rewarding because it fulfills a biological need, such as hunger or thirst. Food, water, and shelter are all considered primary reinforcers because they are necessary for survival and provide immediate satisfaction of basic needs.

In contrast, money does not fulfill a biological need directly. Instead, it serves as a secondary reinforcer, which gains its value from being associated with primary reinforcers. Money can be exchanged for food, water, shelter, and other resources, but it does not provide these necessities itself. Thus, it does not qualify as a primary reinforcer. Understanding this distinction between primary and secondary reinforcers is crucial in behavioral psychology, as it affects how behaviors are motivated and maintained.