What is a defining characteristic of public goods?

A defining characteristic of public goods is that they are nonexcludable and nonrival. Nonexcludability means that once the good is provided, it is not possible to prevent anyone from using it. This encourages people to benefit from the good without necessarily paying for it, leading to challenges such as the "free rider" problem, where individuals may avoid contributing to the provision of the good while still enjoying its benefits.

Nonrivalry indicates that one person's use of the good does not diminish the ability of others to use it as well. A classic example of a public good is national defense; one person's protection from invasion does not reduce the protection available to others. These characteristics contribute to the need for government provision or regulation of public goods, as market mechanisms may fail to supply them in sufficient quantities.

The other options describe different types of goods. For instance, excludable and rival goods refer to private goods where individuals can be prevented from using them, and one person's use reduces availability to others. Understanding these distinctions is essential in microeconomics when analyzing how different goods are provided and consumed in society.