1. the elasticity of supply and the slope are both infinite.
2. the elasticity of supply and the slope are both zero.
3. the elasticity of supply is infinite and the slope zero.
4. the elasticity of supply is zero and the slope infinite.
Choose the option that yields the correct answer.
Option 4 is the correct answer. Recall that
Ψ = ( ΔQ / Q ) / ( ΔP / P ) = P / θ Q
where θ is the slope of the curve and Ψ is the elasticity. When the curve is vertical the slope (rise divided by run) is infinite. Since the denominator of the above equation for Ψ is therefore infinite, Ψ must be zero.