One of the best examples of a public good is national defense. To the extent one person in a geographic area is defended from foreign attack or invasion, other people in that same area are likely defended also. This makes it hard to charge people for defense, which means that defense faces the classic free-rider problem. Indeed, almost all economists are convinced that the only way to provide a sufficient level of defense is to have government do it and fund defense with taxes. ~ Hope this helped!
The second aspect of public goods is what economists call “nonrivalrous consumption.” ... If the good is excludable, private entrepreneurs will try to serve as many fee-paying customers as possible, charging lower prices to some customers if need be. One of the best examples of a public good is national defense.
