c
When a wire is stretched work is done against the interatomic forces. This work is stored in the wire in the form of elastic potential energy.

\(W=\frac{1}{2} \times\) stress \(\times\) strain \(\times\) volume of wire

Also, when strain in small, ratio of longitudinal stress to corresponding longitudinal strain is called Young's modulus of material of body.

\(Y=\frac{\text { longitudinal stress }}{\text { longitudinal strain }}\)

\(W=\frac{1}{2} \times \text { stress } \times \frac{\text { stress }}{Y} \times \text { volume }\)

\(W=\frac{(\text {stress)}^2 \times \text { volume }}{2 Y}\)