A public good is a good that is non-rivalrous, meaning that one person's consumption of the good does not diminish another person's consumption of the same good, and non-excludable, meaning that it is impossible to prevent people from consuming the good.

National defense is a public good because it is non-rivalrous (one person's consumption of national defense does not diminish another person's consumption of national defense) and non-excludable (it is impossible to prevent people from consuming national defense).

The free rider problem arises when people can consume a public good without paying for it. This can lead to a situation where the public good is underprovided, as people are not willing to pay for a good that they can consume for free.

The free rider problem can be solved by providing the public good through the government. This is because the government has the power to tax people and use the tax revenue to pay for public goods.

The tragedy of the commons is the problem that arises when a common resource is overused. This can happen when each individual has an incentive to overuse the resource, even though they know that this will lead to the resource being depleted.

A forest is a common resource because it is non-rivalrous (one person's use of the forest does not diminish another person's use of the forest) and non-excludable (it is impossible to prevent people from using the forest).

The tragedy of the commons can be solved by creating a system of tradable permits. This system allows individuals to trade their rights to use the common resource, which can help to prevent the resource from being overused.

Public goods are non-rivalrous and non-excludable, while private goods are rivalrous and excludable. This means that one person's consumption of a public good does not diminish another person's consumption of the same good, and it is impossible to prevent people from consuming a public good. In contrast, one person's consumption of a private good does diminish another person's consumption of the same good, and it is possible to prevent people from consuming a private good.

The three main characteristics of a public good are non-rivalrous, non-excludable, and decreasing marginal cost. This means that one person's consumption of a public good does not diminish another person's consumption of the same good, it is impossible to prevent people from consuming a public good, and the marginal cost of providing a public good decreases as more people consume the good.

A public good is an example of a decreasing marginal cost good. This is because the marginal cost of providing a public good decreases as more people consume the good. This is because the fixed costs of providing the good are spread over a larger number of people.

A pure public good is non-rivalrous and non-excludable, while an impure public good is rivalrous and non-excludable. This means that one person's consumption of a pure public good does not diminish another person's consumption of the same good, and it is impossible to prevent people from consuming a pure public good. In contrast, one person's consumption of an impure public good does diminish another person's consumption of the same good, and it is possible to prevent people from consuming an impure public good.

A public park is an example of an impure public good. This is because one person's use of a public park does diminish another person's use of the same park, and it is possible to prevent people from using a public park.

The role of government in providing public goods is to provide public goods that the private sector cannot or will not provide. This is because the private sector has no incentive to provide public goods, as it cannot charge people for consuming public goods.

The challenges associated with providing public goods include the free rider problem, the tragedy of the commons, and the difficulty of determining the optimal level of provision. The free rider problem is the problem that arises when people can consume a public good without paying for it. The tragedy of the commons is the problem that arises when a common resource is overused. The difficulty of determining the optimal level of provision is the problem that arises when it is difficult to determine how much of a public good should be provided.