Stress \(=\) Elastic limit

\(\delta_{\text {max }}=\frac{\sigma_{\text {elastlc }} \times L}{\text { Young's modulus }}=\frac{8 \times 10^8 \times 1}{2 \times 10^{11}}  =4 \times 10^{-3}\)

\(=4 \mathrm{~mm}\)

i.e. maximum elongation is \(4 \mathrm{~mm}\)