In which reaction will the point of equilibrium shift to the left when the pressure on the system is increased

Question

A. C(s) + O2(g) ↔ CO2(g)
B. CaCO3(s) ↔ CaO(s) + CO2(g)
C. 2Mg(s) + O2(g) ↔ 2MgO(s)
D. 2H2(g) + O2(g) ↔ 2H2O(g)

Answer 1

Probably B. Increasing the pressure tends to drive the reaction in which ever direction of reduces the amount of gas present; either by combining 2 or more gases into one, or combining a gas with a solid or liquid to make a solid or liquid. If the stoicometry shows equal equivalents of gas on either side there will be little or no effect.