To solve this problem, we need to analyze the thermodynamics of the reaction $2$Cl$(g) \rightarrow$Cl$_2(g). \\$1. Enthalpy Change $(\Delta_r H): \\$• The reaction involves the formation of a $$Cl$_2$ molecule from two Cl atoms.$\\$• Bond formation releases energy, which means the process is exothermic.$\\$• Therefore, $\Delta_r H < 0. \\$2. Entropy Change $(\Delta_r S): \\$• Entropy is a measure of disorder.$\\$• In the reaction, two moles of gaseous atoms (Cl) combine to form one mole of a diatomic molecule $($Cl$_2). \\$• This results in a decrease in the number of gas particles, leading to a decrease in disorder.$\\$• Therefore, $\Delta_r S < 0. \\$Based on the above analysis, the correct option is:$\\$Option 3: $\Delta_r H < 0$ and $\Delta_r S < 0.$