For the reaction, $2\mathrm{Cl}\left(\mathrm{g}\right)\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)$, the correct option is

$2\mathrm{Cl}\left(\mathrm{g}\right)⟶{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

In this reaction number of gaseous mole decreases hence entropy decreases, ${\mathrm{\Delta }}_{\mathrm{r}}\mathrm{S}<0$ 

Decomposition of ${\mathrm{Cl}}_2$ into gaseous atoms is an endothermic process. Therefore, its reverse is an exothermic process,  ${\mathrm{\Delta }}_{\mathrm{r}}\mathrm{H}<0$