Defense of the nation is a service provided by our armed forces. This service is.

Public good which is non-rival and non-excludable in consumption.

The correct answer is Option (2) → Public good which is non-rival and non-excludable in consumption.

• Rivalry in Consumption: A good is rival if one person's consumption of it prevents or diminishes another person's consumption. For example, if you eat a slice of pizza, no one else can eat that same slice. National defense, however, is non-rival. The protection afforded to one citizen by the armed forces does not reduce the protection afforded to any other citizen. Everyone in the nation benefits simultaneously from the defense provided.

• Excludability in Consumption: A good is excludable if it is possible to prevent people who have not paid for it from consuming it. For instance, you can be excluded from watching a movie in a cinema if you don't buy a ticket. National defense is non-excludable. It is practically impossible to exclude any citizen within the nation's borders from receiving the benefits of national defense, even if they don't contribute directly (e.g., through taxes).

Since national defense is both non-rival and non-excludable in consumption, it is classified as a public good.