Identify the limiting reagent and the volume of CO2 formed when 11L Cs2 reacts with 18L O2 to produce CO2 gas?

No need to do any major calculations here. Since PV=nRT, we can see that volumes of a gas are proportional to the number of moles present. Therefore, in order for all of the CS2 to be reacted, by the stoichiometry of the reaction, 11 L * 3 = 33 L if O2 needs to be available. Since there is only 18 L of O2, it must be the limiting reagent: the answer is b). The bottom two are products, not reagents, so their being on the list of answers is silly.