If there is no change in the quantity demanded of good X with a change in the price of good X, then the price elasticity of demand for good X is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Perfectly inelastic
Price elasticity of demand (eD) measures how strongly the quantity demanded responds to a change in price. If the quantity does not change at any price, eD is 0. The demand curve is then a vertical line. Such demand is called perfectly inelastic.
Option (1) Perfectly elastic — Incorrect. The demand curve is a horizontal line at one price, and eD is infinite. At any other price, the quantity demanded drops to zero.
Option (2) Perfectly inelastic — Correct. A change in price never changes the quantity demanded, so eD is 0.
Option (3) Unitary elastic — Incorrect. The percentage change in quantity equals the percentage change in price, so eD is 1.
Option (4) Greater than 1 — Incorrect. The percentage change in quantity is more than the percentage change in price. Such demand is called elastic.
NCERT (2026-27): Introductory Microeconomics — Chapter 2: Theory of Consumer Behaviour
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