What does a supply curve illustrate?

A supply curve illustrates the quantity supplied at various prices, showcasing how producers are willing to supply more of a good or service as its price increases, all else being equal. This relationship typically reflects the basic law of supply, indicating that higher prices provide an incentive for producers to increase their output.

By plotting the prices on the vertical axis and the quantities supplied on the horizontal axis, the supply curve usually slopes upwards from left to right, demonstrating that as prices rise, the quantity of goods supplied also tends to rise.

In this context, the other options focus on different aspects of economic relationships. For example, while the relationship between demand and total revenue relates more to consumer choices and market behavior, and the optimal production level addresses the efficiency of production decisions, they do not specifically represent what a supply curve illustrates. Changes in market equilibrium involve the interaction of both supply and demand, but again, this is not the direct representation of a supply curve alone.