Final answer:
If the concentration of carbon monoxide is doubled in a reaction that is second order in CO, the reaction rate will increase by a factor of 4.
Step-by-step explanation:
When a reaction is found to be second order in carbon monoxide (CO) concentration, it means that the rate of the reaction is directly proportional to the square of the concentration of CO. Therefore, if the concentration of CO is doubled, with everything else kept the same, the reaction rate increases by a factor of 4. This is because the new rate is proportional to (2[CO])2, which is 4 times the original concentration squared ([CO]2).