What does a demand curve illustrate?

A demand curve clearly illustrates the relationship between price and quantity demanded for a good or service. Specifically, it shows how the quantity of a product that consumers are willing and able to purchase changes in response to variations in its price, holding all else constant. The typical downward slope of the demand curve indicates that, as the price of the good decreases, the quantity demanded generally increases, and conversely, as the price increases, the quantity demanded typically decreases. This fundamental principle underlies much of microeconomic theory and helps explain consumer behavior in the market.

The other options focus on different economic relationships. The option regarding the relationship between income and consumption pertains more to income elasticity and consumer choice theory, while the relationship between supply and demand is broader and does not specifically pertain to the function of a demand curve alone. Lastly, the relationship between production and industry growth relates to macroeconomic factors and not directly to demand characteristics depicted by the demand curve.