Define non-excludability and give an example.

• A. Non-excludability means it’s easy to prevent usage; example: private library.
• B. Non-excludability means it’s difficult to prevent people from using the good; example: toll road.
• C. Non-excludability means one person’s use does not restrict another’s; example: shared bicycle.
• D. Non-excludability means it’s difficult to prevent people from using the good; example: national defense.

Answer: (D)

Non-excludability means it’s difficult or costly to prevent people from using a good, so many can enjoy it even if they don’t pay. A classic example is national defense: once defense is provided, you can’t realistically exclude some residents from being protected or charge them separately, so everyone benefits whether they pay or not. This is why such goods are typically supplied by the government and why markets often underprovide them.

The other options miss the essence: a private library is easy to exclude users (you need a membership), a toll road is also excludable (you pay to use it), and a shared bicycle system is generally excludable and rival (availability depends on paying users and you can’t access it freely).