What effect would a change in price of a commodity have on its supply?

1. Analyze the question The question asks what happens to supply when the price of the commodity itself changes. The key is knowing the difference between a change in supply and a change in quantity supplied.

2. Explain the concept

• Change in quantity supplied: This is caused only by a change in the commodity's own price. It is shown as a movement along the same supply curve (an extension or contraction of supply).
• Change in supply: This is caused by non-price factors such as cost of production, technology, taxes and subsidies, weather, and the number of sellers. It is shown as a shift of the whole supply curve (an increase or decrease in supply).

3. Step-by-step solution

• If the price rises, producers are willing to offer more for sale, so the quantity supplied increases (movement up along the curve).
• If the price falls, the quantity supplied decreases (movement down along the curve).
• In both cases the supply curve itself does not shift. So the supply schedule stays the same, and only the quantity supplied changes.

Checking the options:

• A. An increase in supply: this would need a shift of the curve caused by non-price factors. ✗
• B. No change in supply: this is partly true in the strict sense, because the curve does not shift. But it ignores that the quantity supplied does change, so it is incomplete. ✗
• C. A decrease in supply: this is also a curve shift. ✗
• D. A change in the quantity supplied: this is the correct description of a movement along the curve caused by a price change. ✓

4. Answer The correct option is D. A change in the quantity supplied.

5. Exam tip Remember: "Own price changes → move along the curve (quantity supplied). Anything else changes → shift the curve (supply)." JAMB often tests the wording "change in supply" versus "change in quantity supplied", so read it carefully.