If 0.400 moles CO and 0.400 moles O2 completely react, 17.604 grams of CO2 would be produced.
First, let us look at the balanced equation of reaction:

According to the equation, the mole ratio of CO and O2 is 2:1. But in reality, the mole ratio supplied is 1:1. Thus, CO is the limiting reactant while O2 is in excess.
Also from the equation, the ratio of CO consumed to that of CO2 produced is 1:1. Thus, 0.400 moles of CO2 would also be produced from 0.400 moles of CO.
Recall that: mole = mass/molar mass
Therefore, the mass in grams of CO2 that would be produced from 0.400 moles can be calculated as:
Mass = mole x molar mass
= 0.400 x 44.01
= 17.604 grams
More on calculating mass from number of moles can be found here: brainly.com/question/12513822