Which statement describes a public good?

• A. It is excludable and not rival; example cable TV
• B. It is not excludable and not rival; example national defense
• C. It is excludable and rival; example private road
• D. It is not excludable but rival; example street lighting

Answer: (B)

Public goods are defined by two properties: non-excludability and non-rivalry. That means once the good is provided, you can’t easily prevent people from benefiting, and one person’s use does not reduce another’s ability to use it. National defense is the classic example: everyone in the country benefits, and protecting one person doesn’t diminish protection for others. Because markets struggle to supply goods that people can’t be easily charged for or that everyone uses without reducing others’ consumption, governments often provide public goods.

This description—not excludable and not rival, with national defense as the example—best fits a public good. The other options describe different types of goods: excludable and non-rival (club or information goods like cable TV), excludable and rival (private goods like a private road), or not excludable but rival (a common resource such as certain scarce fisheries or street lighting when overused).