When $T _1=100\,N$, Extension $=\ell_1-\ell_0$
When $T _2=120\,N$, Extension $=\ell_2-\ell_0$
Then $100= K \left(\ell_1-\ell_0\right)$
And $120= K \left(\ell_2-\ell_0\right)$
$\frac{1}{2} \Rightarrow \frac{5}{6}=\frac{\ell_1-\ell_0}{\ell_2-\ell_0}$
$5 \ell_2-5 \ell_0=6 \ell_1-6 \ell_0$
$\ell_0=6 \ell_1-5 \ell_2$
$\ell_0=6 \ell_1-5\left(\frac{11 \ell_1}{10}\right)$
$\ell_0=6 \ell_1-\frac{11 \ell_1}{2}$
$\ell_0=\frac{\ell_1}{2}$
$\therefore x=2$


| Column $-I$ | Column $-II$ |
| $(a)$ Stress $\propto $ Strain | $(i)$ $M^1\,L^{-1}\,T^{-2}$ |
| $(b)$ Dimensional formula for compressibility | $(ii)$ $M^{-1}\,L^{1}\,T^{-2}$ |
| $(iii)$ Poisson’s ratio | |
| $(iv)$ Hooke’s law |