There are two containers filled with gases. In both containers, gases are at the same temperature and presssure. The first container is 3 L and contains 0.9 moles of gas. The second container is 1 L. How many moles of gas are there in the second container?

Answer 1

If p is same and T is same then mols is proportional to volume.
If you have 1/3 the volume you must have 1/3 the mols.