Unit Elastic Supply Curve Identification

Steps:

• Recall price elasticity of supply (PES) measures percentage change in quantity supplied divided by percentage change in price; PES = 1 means unit elastic.
• Identify that a unit elastic supply curve has constant PES of 1 at all quantities, appearing as a straight line from the origin (45-degree ray) where quantity is proportional to price.
• Examine each curve: horizontal lines indicate infinite PES, vertical lines zero PES, lines not through origin varying PES, and origin-ray constant PES=1.
• Select the curve matching the origin-ray shape.

Why A is correct:

• Curve A is a straight line through the origin, satisfying PES = (%ΔQ)/(%ΔP) = 1 for all points, as slope equals elasticity along such rays.

Why the others are wrong:

• B: Upward-sloping line not through origin, yielding PES >1 at high quantities and <1 at low.
• C: Steeply sloped curve, indicating PES <1 overall due to low responsiveness.
• D: Flat curve, showing infinite PES as quantity changes greatly with small price shifts.

Final answer: A