b
Stress $=1.5 \mathrm{kg} . \mathrm{wt} / \mathrm{mm}^{2}$
$Y=5 \times 10$
$\frac{\Delta \ell}{\ell}=\frac{\text { Stress }}{\mathrm{Y}}$
$\frac{\Delta \ell}{\ell}=\frac{1.5 \times 10^{6} \times 10}{5 \times 10^{11}} \times 100$
$\frac{\Delta \ell}{\ell}=3 \times 10^{-3} \%$