Final answer:
When more MgO is added to the system, the reaction will shift to the left, decreasing the concentration of MgO and increasing the amount of Mg(OH)2.
Step-by-step explanation:
The reaction will shift to the left. When more MgO is added to the system, the concentration of MgO increases. According to Le Chatelier's principle, the system will try to counteract this change by shifting the equilibrium in the direction that consumes the excess MgO. Therefore, the reaction will shift to the left, decreasing the concentration of MgO and increasing the amount of Mg(OH)2.