Which of the following can be classified as an additive reinforcer?

An additive reinforcer is something that, when added following a behavior, increases the likelihood of that behavior being repeated in the future. Activity is considered an additive reinforcer because it involves the addition of something desirable or enjoyable after the desired behavior occurs. For instance, if a child completes their homework and is then allowed to play outside or engage in a favorite game, that "activity" serves as a reward that encourages them to continue to perform the behavior of completing homework in the future.

In contrast, shock would be indicative of aversive reinforcement, where an unpleasant stimulus is used, and negative feedback typically focuses on correcting behavior rather than encouraging it. Both of these do not meet the criteria for an additive reinforcer as they do not enhance the likelihood of the targeted behavior being repeated through reward. Therefore, the best example of an additive reinforcer in this context is activity.