Which equation best expresses the relationship between pressure and volume for gas?

It won't be possible for me to answer this question if there is no context. I tried to find a similar question and I came up with one. The problem is shown in the attached picture. From the given choices, all their units are atm*mL. So, that means that P*V. The answer could only be (2) or (4). Let's try the data in the table to find out.

PV = (0.5 atm)(1000 mL) = 500 atm*mL
PV = (1 atm)(500 mL) = 500 atm*mL
PV = (2 atm)(250 mL) = 500 atm*mL

Thus, the answer is choice (2).