$2 CaO + Cl _{2} \stackrel{\text { Red hot }}{\longrightarrow } CaCl _{2}+ O _{2} \uparrow$
From Arrhenius equation
$\ln \frac{k_{2}}{k_{1}}=\frac{E_{a}}{R}\left[\frac{1}{T_{1}}-\frac{1}{T_{2}}\right]$
or $\ln \frac{k_{2}}{k_{1}}=\frac{600 R}{R}\left(\frac{1}{300}-\frac{1}{600}\right)$
or $\ln \frac{k_{2}}{k_{1}}=600\left(\frac{2-1}{600}\right)$
or $\ln \frac{k_{2}}{k_{1}}=1$ or $\frac{k_{2}}{k_{1}}=e$