Final answer:
A gym membership is an example of a club good because it is excludable while remaining non-rival as long as space is available.
Therefore, the correct answer is: option 4) Club good
Step-by-step explanation:
A gym membership that always has space in classes and on machines is an example of a club good.
Unlike a public good, a club good is excludable because the gym can prevent non-members from using the facilities.
Yet, it is non-rival since one person's use does not significantly affect another's (assuming there is always space).
In contrast, a public good is both non-excludable and non-rival, such as national defense or public parks, where it is not feasible or practical to prevent anyone from using the good, and one person's use does not diminish the availability to others.
A club good is a type of good that is excludable, meaning that the owners or operators of the gym can control who has access to the facilities. However, it is not rivalrous, as one person's use of the gym does not prevent others from using it.