The table gives the initial length ${\mathcal{l}}_0$ , change in temperature $∆T$ and change in length $∆\mathcal{l}$ of four rods. Which rod has greatest coefficient of linear expansion

$∆\mathcal{l}={\mathcal{l}}_0\alpha ∆T$

$\alpha =\frac{∆\mathcal{l}}{{\mathcal{l}}_0∆T}$

where 

${\mathcal{l}}_0$ $\to$initial length

$∆T\to$change in temperature

$∆\mathcal{l}\to$change in length of four rods

$\alpha \to$coefficient of linear expansion

${\alpha }_1=\frac{1}{1\times 100}={10}^{-2}$

${\alpha }_2=\frac{2}{100}=2\times {10}^{-2}$

${\alpha }_3=\frac{3}{1.5\times 50}=4\times {10}^{-2}$

${\alpha }_4=\frac{4}{2.5\times 20}=8\times {10}^{-2}$ (maximum)