(i) An Economic Model is a simplified version of reality or it is a simplified, often mathematical, framework designed to illustrate complex processes.
(ii) The production possibility frontier (PPF) is a curve depicting all maximum output possibilities for two goods, given a set of inputs consisting of resources and other factors.
(iii) Opportunity cost is the benefit that is missed or given up when an investor, individual or business chooses one alternative over another.
(iv) Scarcity is the economic problem of having unlimited human wants and needs in a world of limited resources.