Final answer:
Option (4), In operant conditioning, extinction occurs when a previously reinforced behavior is no longer reinforced, leading to a decrease in that behavior.
Step-by-step explanation:
In operant conditioning, extinction results from the repeated performance of operant behavior in the absence of reinforcement. This process occurs when the association between the behavior and the reinforcement that it normally produces is severed over time because the reinforcement is no longer provided.
For instance, if a behavior was previously reinforced on a fixed interval schedule, such as receiving medication after pressing a button, and this reinforcement stops, the behavior will eventually decrease in frequency and may stop altogether. In contrast to reinforcement, which serves to increase the likelihood of a behavioral response, extinction diminishes the conditioned behavior as it is no longer rewarded.