The answer is b, because if it gets colder then means more heat is exiting than it is entering.
If the reaction is represented by:
PCl₃ + Cl₂ <-> PCl₅ (exothermic)
the mole fraction of chlorine in the equilibrium mixture will change according to the following:
Decrease the volume: decrease
Increase the temperature: increase
Increase the volume: increase
Decrease the temperature: decrease
Explanation:
HCL you can do it yourself .try again
