$=\frac{1}{2} \times Y \times(\alpha \Delta \theta)^{2}$
$=\frac{1}{2} \times 10^{11} \times\left(12 \times 10^{-6} \times 20\right)^{2}=2880 \mathrm{J} / \mathrm{m}^{3}$

| Column $-I$ | Column $-II$ |
|
$(a)$ Stress is proportional to strain. |
$(i)$ Elastic limit |
| $(b)$ When the load of the wire is removed, the body does regain its original dimension. | $(ii)$ Limit of pro-portionality |
| $(iii)$ Plastic deformation |

Assertion $A$: Steel is used in the construction of buildings and bridges.
Reason $R:$ Steel is more elastic and its elastic limit is high.
In the light of above statements, choose the most appropriate answer from the options given below