Answer: Increase in temperature
Explanation:
Once there is an increase in temperature of the exothermic reaction, the equilibrium position shifts to the left since equilibrium constant, K decreases; hence favoring the formation of reactants which are 2SO2(g) and O2(g).
Decrease in temperature, on the other hand, would shift the equilibrium to the right since equilibrium constant, K increases.
Thus, for the exothermic reaction 2SO2(g)+O2(g)=2SO3(g): increase in temperature would shift the equilibrium over to the left.
