Question

if a demand curve for a good were completely vertical, it would be considered:
a. unitary elastic.
b. perfectly inelastic.
c. relatively inelastic.
d. perfectly elastic.

Explanation:

A completely vertical demand curve means the quantity demanded of a good does not change at all, regardless of any change in the good's price. This matches the definition of perfectly inelastic demand, where price elasticity of demand equals 0. Unitary elastic means elasticity is 1 (quantity changes proportionally to price), relatively inelastic means quantity changes less than proportionally to price (curve is steep but not vertical), and perfectly elastic is a horizontal curve (quantity demanded drops to 0 at any price increase).

Answer:

b. perfectly inelastic.