Final answer:
When the price of apples increases, the quantity demanded for apples decreases, but the demand curve does not shift. Consumers buy fewer apples at the higher price, potentially increasing demand for substitute goods like peaches.
Step-by-step explanation:
The question pertains to how the demand or quantity demanded for apples changes when their price increases and considering that peaches are substitutes for apples. In economic terms, when the price of a product increases, the quantity demanded (Qd) for that product typically decreases because consumers will buy less of it at the higher price.
However, the overall demand (D) curve remains the same unless there is a change in non-price determinants, such as consumer preferences, incomes, or the prices of substitute goods. In this scenario, peaches are substitutes; therefore, if the price of apples goes up and all else is constant, consumers will buy more peaches instead, leading to an increased demand for peaches but not affecting the demand for apples.
Instead, there will be a decrease in the quantity demanded for apples. So the correct answer in this case is (d) Quantity demanded (Qd) decreases.