Final answer:
To increase the concentration of CO at equilibrium in the reaction, you can increase the concentration of CO2 or decrease the concentration of O2.
Step-by-step explanation:
To increase the concentration of CO at equilibrium in the reaction 2 CO2(g) + heat → 2 CO(g) + O2(g), you can increase the concentration of CO2 or decrease the concentration of O2. By Le Chatelier's principle, if you increase the concentration of a reactant (CO2), the equilibrium will shift in the direction that consumes that reactant (towards CO and O2). Similarly, if you decrease the concentration of a product (O2), the equilibrium will shift towards the side that produces that product (CO).