When a good or productive factor is completely fixed in quantity regardless of the market price, what is the shape of its supply curve?

Introduction / Context:
Supply analysis in microeconomics often assumes that the quantity supplied of a good varies with its price. However, there are special cases where the quantity of a good or factor is completely fixed, at least in the short run. This question asks you to recall the shape of the supply curve when the quantity of a good cannot change regardless of price, which is a classic textbook example for perfectly inelastic supply.

Given Data / Assumptions:

• The total quantity of the good or productive factor is fixed.
• Producers cannot increase or decrease the available quantity in response to price changes.
• We are considering the relationship between price on the vertical axis and quantity supplied on the horizontal axis.
• The focus is on the shape of the supply curve under these conditions.

Concept / Approach:
When the quantity supplied of a good is completely unresponsive to price, the supply is said to be perfectly inelastic. Graphically, a perfectly inelastic supply curve is drawn as a vertical line at the given fixed quantity. No matter what the price is, the quantity supplied remains the same. Examples include the supply of land in a given region or the supply of a unique painting by a famous artist. In contrast, a horizontal supply curve would represent perfectly elastic supply, where suppliers are willing to supply any quantity at a given price but none at any other price.

Step-by-Step Solution:
Step 1: Identify that the key condition is “completely fixed in amount, regardless of price”. Step 2: Recall that when quantity cannot change as price changes, supply is perfectly inelastic. Step 3: Remember that a perfectly inelastic supply curve is drawn as a vertical line at the fixed quantity on the horizontal axis. Step 4: Match this description to the option that says the supply curve is vertical.

Verification / Alternative check:
A quick mental diagram can confirm this. Place quantity on the horizontal axis and price on the vertical axis. If quantity is fixed at Q0, draw a line at Q0 that does not move left or right as price changes. This line is vertical. Any upward sloping or downward sloping curve would imply that quantity changes with price, which contradicts the given condition.

Why Other Options Are Wrong:
Downward sloping to the right: This would indicate an inverse relationship between price and quantity supplied, which is not typical for supply and is also inconsistent with fixed quantity.
Horizontal: A horizontal supply curve implies that quantity supplied can change freely at a fixed price, which is the opposite of a completely fixed quantity.
Upward sloping to the right: This is the usual case for supply when quantity responds positively to price, but here quantity is not allowed to change at all, so this is wrong.

Common Pitfalls:
Students sometimes mix up the shapes for perfectly elastic and perfectly inelastic curves, confusing vertical with horizontal. A useful memory aid is that “inelastic” suggests “no movement” in quantity, which is represented by a vertical line at a fixed quantity. Also, some learners assume supply must always slope upward, forgetting that special cases like fixed factor supply are important exceptions in theory and in some real markets.

Final Answer:
When the quantity of a good or factor is completely fixed regardless of price, the supply curve is vertical.