Which of the following defines a public good?

A public good is defined as a good that is non-excludable and non-rivalrous. This means that individuals cannot be effectively excluded from using the good, and one person's consumption does not diminish the availability of the good for others.

For example, public goods include things like national defense, clean air, and public parks. Everyone can benefit from these goods, and one person's use of them does not reduce the ability of others to use them simultaneously. This characteristic leads to the concept of the "free rider problem," where individuals may benefit from the good without contributing to its cost, since they cannot be excluded from its use.

The other options describe characteristics that do not align with the definition of a public good. A product that can only be consumed by one person at a time is known as a private good, as it is excludable and rivalrous. Goods provided solely by private businesses don't meet the criteria of being public goods because they often turn a profit and can be restricted from certain individuals. Lastly, the definition of a good that is excludable and rivalrous also aligns with private goods, which further clarifies why the correct answer centers on non-excludable and non-rivalrous attributes.