There is zero opportunity cost, for example air. An economic good is a commodity in limited supply. Expenditure on producer or capital goods is called investment. The economic problem refers to the scarcity of commodities. There is only a limited amount of resources available to produce the unlimited amount of goods and services we desire.
Society has to decide which commodities to make.
We have to decide how to make those commodities. The opportunity cost principle states the cost of one good in terms of the next best alternative. For example, a gardener decides to grow carrots on his allotment. Further examples are given in Table 1.2. Different countries have different methods of tackling the economic problem.