The balanced reaction would be:
2CO + O2 = 2CO2
We assume that the gases are ideal gas so that we use the relation that 1 mol of an ideal gas is equal to 22.4 L of the gas at STP. From that relation, we get the number of moles and we can convert it to other units. We do as follows:
1.0 L CO ( 1 mol / 22.4 L ) ( 2 mol CO2 / 2mol CO ) = 0.045 mol CO2 produced
0.045 mol CO2 ( 22.4 L / 1 mol ) = 1 L of CO2
0.045 mol CO2 ( 44.01 g / 1 mol ) = 1.98 g of CO2
