Three of the following demand curves have the same price elasticity at every point on them. Which one is the odd one out?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A straight-line demand curve that meets both axes
On a straight-line demand curve, elasticity changes from point to point: 0 where it meets the quantity axis, 1 at the midpoint, and infinity where it meets the price axis.
Option (1) A straight-line demand curve that meets both axes — Odd one out. Its elasticity is different at every point.
Option (2) A vertical demand curve — Same elasticity throughout. Demand never changes with price, so elasticity is 0 everywhere.
Option (3) A horizontal demand curve — Same elasticity throughout. At any other price demand drops to zero, so elasticity is infinite everywhere.
Option (4) A demand curve shaped as a rectangular hyperbola — Same elasticity throughout. Price times quantity stays the same, so elasticity is 1 everywhere.
NCERT (2026-27): “Constant Elasticity Demand Curve The elasticity of demand on different points on a linear demand curve is different varying from 0 to ∞. But sometimes, the demand curves can be such that the elasticity of demand remains constant throughout. Consider, for example, a vertical demand curve as the one depicted in Figure 2.20(a). … A price never leads to a change in the demand for such a demand curve and |eD| is always 0. Therefore, a vertical demand curve is perfectly inelastic. … A horizontal demand curve is perfectly elastic. …” “Figure 2.20(c) depicts a demand curve which has the shape of a rectangular hyperbola. This demand curve has a property that a percentage change in price along the demand curve always leads to equal percentage change in quantity. Therefore, |eD| = 1 at every point on this demand curve. This demand curve is called the unitary elastic demand curve.” |