Which of the following is a fixed schedule of reinforcement?

A fixed schedule of reinforcement refers to a scenario where a reinforcer is delivered after a specific number of responses or a specific amount of time has passed. In the case of providing reinforcement after every fifth response, it is a clear example of a fixed ratio schedule, where the number of responses needed for reinforcement remains constant.

This schedule creates a predictable pattern for the individual receiving the reinforcement, which can enhance motivation and learning. Individuals can easily anticipate when they will receive reinforcement, thereby influencing their behavior to achieve the desired response.

On the other hand, the other options describe schedules of reinforcement that are not fixed. Varying time intervals or random reinforcement show variability that does not lend itself to the predictability seen in fixed schedules, making them different types of reinforcement schedules entirely. This highlights the importance of understanding the distinction between fixed and variable reinforcement schedules in the context of behavior modification and motivation strategies.