Question

For a perfect elastic body, Young’s modulus is(a) zero (b) infinity(c) 1 (d) –1

Answer 1

The answer is (b) infinity. Young's modulus is equivalent to longitudinal stress divided by the strain, this is described as:
Young’s modulus = stress/strain = (FL0)/A(Ln − L0).
For a perfect elastic body: 
When stress is applied then similarly the stain would increase too leading to a linear graph 
This means an infinite linear line is formed when evaluating Young's modulus of a perfect elastic body. 

Answer 2

Young modulus is

Infinity option b