Which of the following is an example of a private good?

A private good is characterized by two main features: it is both excludable and rivalrous. Excludable means that people can be prevented from using the good if they do not pay for it. Rivalrous indicates that one person's use of the good reduces the ability of another person to use it.

Gasoline is an excellent example of a private good. It is excludable because gas stations can charge customers and restrict access to individuals who haven’t paid for it. It is also rivalrous because when one person purchases and uses gasoline, that specific quantity of gasoline is no longer available for others to use.

In contrast, national parks and public schools are typically examples of public goods. National parks provide collective benefits and are often funded by taxation, meaning they are accessible to all regardless of payment, while public schools cater to a broader public interest, funded predominantly through taxes. Clean air is more of a common resource, as it is available to everyone and one person's consumption does not generally prevent others from enjoying it. However, it can also become congested or diminished through pollution, making it less clear-cut than the definition of private goods.