Which economic idea emphasizes the balance between supply and demand in a free market?

The concept that emphasizes the balance between supply and demand in a free market is market equilibrium. Market equilibrium occurs when the quantity of goods supplied equals the quantity of goods demanded at a certain price level. This point is crucial because it represents the state in which the market forces are balanced, and there is no inherent pressure for the price to change, as consumers are purchasing all that is produced.

The invisible hand, while relevant to free market principles, refers more broadly to how individuals pursuing their self-interest can lead to positive societal outcomes, rather than focusing specifically on the intersection of supply and demand. Opportunity cost deals with the value of the next best alternative forgone when making a choice, and scarcity addresses the limited availability of resources in relation to unlimited wants. Both concepts are important in economics but do not directly address the equilibrium between supply and demand.