Which situation would cause the following equilibrium reaction to decrease the formation of products 2so2(g) + o2(g) forward backward arrow 2so43(g) + energy

The reaction is as Follow,

                      2 SO₂  +  O₂    ⇄    2 SO₃    ΔH = -94.58 kJ mol⁻¹

Changing Concentration:
                                           According to Le Chatelier's principle, the removal of SO₂ and O₂ (or decrease in their concentration) at equilibrium will result in decrease in the formation of SO₃.

Changing Pressure:
                                  As the reaction proceeds by the decrease in volume, so by decreasing the pressure will shift the equilibrium in backward direction decreasing the concentration of product.

Changing Pressure:
                               Since the forward reaction is exothermic, the equilibrium will be shifted in backward direction by increasing the temperature.