At a certain temperature and pressure, 0.20 mol of carbon dioxide has a volume of 3.1 L. What does a 3.1-L sample of hydrogen at the same temperature have a volume of?
Do you realize the question you have asked?
I don't criticize, because it is all too easy to make a mistake. We've all done it, and it's funny when you do. You have just asked
I suspect the question meant to ax:
The answer is
At the same temperature and pressure, equal volumes of gases, any gases, contain the same number of molecules. This is Avogadro's Law. And you specify the number of molecules when you specify the number of moles.