Which of the following is an example of an unconditioned reinforcer?

An unconditioned reinforcer, often referred to as a primary reinforcer, is a stimulus that naturally increases the likelihood of a behavior when presented, without prior learning or conditioning. Food is a prime example of an unconditioned reinforcer because it fulfills a biological need—providing sustenance and energy essential for survival. When an individual receives food, it elicits a satisfying response that reinforces behaviors leading to its attainment.

In contrast, the other options, such as money, privacy, and attention, are considered conditioned reinforcers. They acquire their reinforcing properties through association with other primary reinforcers. For instance, money becomes valuable because it can be exchanged for food and other necessities. Privacy and attention similarly gain their reinforcing power through social interactions and experiences, which are learned rather than instinctual. Therefore, food stands out as the correct choice for an unconditioned reinforcer due to its innate ability to reinforce behaviors necessary for survival.