Which of the following illustrates a change in quantity demanded?

• A. An increase in consumer income causes consumers to buy more of the good at every price.
• B. A decrease in the price of the good leads to consumers buying more of it.
• C. A rise in the price of a substitute good increases demand for the good.
• D. A change in consumer preferences increases demand for the good at all prices.

Answer: (B)

Verified step by step guidance

1. Understand the difference between 'change in quantity demanded' and 'change in demand'. A change in quantity demanded refers to movement along the demand curve caused by a change in the price of the good itself, while a change in demand refers to a shift of the entire demand curve caused by factors other than the good's own price.
2. Identify the factor causing the change in each option. For example, an increase in consumer income, a rise in the price of a substitute, or a change in consumer preferences are all factors that shift the demand curve (change in demand).
3. Recognize that a decrease in the price of the good itself leads to a movement along the demand curve, which is a change in quantity demanded, not a shift in demand.
4. Recall the law of demand: when the price of a good decreases, the quantity demanded increases, holding other factors constant. This is the classic example of a change in quantity demanded.
5. Conclude that the correct illustration of a change in quantity demanded is the option where the price of the good changes and consumers buy more of it, reflecting movement along the demand curve.