Answer:
The correct option is 1. The reinforcer is presented ONLY if the subject responds (but not necessarily every time the subject responds).
Explanation:
Operant conditioning was developed by B. F. Skinner with the belief that it is possible to teach new behaviors if those behaviors are properly reinforced. As we know, when we talk of reinforcement, we can have positive or negative reinforcers, which does not mean they are good or bad. A positive reinforcer happens when something is added to increase the probability of a behavior. A negative one happens when something is removed to increase the probability of a behavior.
In operant conditioning, the reinforcer is presented ONLY if the subject responds with the targeted behavior. That does not mean every time the subject responds he will receive reinforcement. In natural occurring situations, for instance, it is not likely that it will happen every time - such as receiving a compliment from your boss every time you do a good job is unlikely. In controlled situations, there will certainly be a reinforcement schedule. In some cases, it might happen every time, in others, it might not.
