The concentration of chlorine will increase due to the addition of CO to the system as it will shift the equilibrium towards the formation of more Cl2. This is in accordance with Le Chatelier's principle. The equilibrium expression for the reaction is:
Kc = [COCl2][Cl2] / [CO][Cl2]
When CO is added, its concentration in the denominator will increase, and the system will shift to the right to consume some of the added CO. This will result in an increase in the concentrations of COCl2 and Cl2, and a decrease in the concentration of CO. Therefore, the concentration of chlorine will increase.
