as level chemsitryWatch
At contstant temperature PV = constant, so a plot of PV against increasing pressure should be a flat straight line. The gas that deviates furthest from this "ideal" situation is the "least" ideal
One of the assumptions of an ideal gas is that there is negligible intermolecular forces of attraction (IMF) between the gaseous particles. To achieve that, we either increase the volume (or decrease the pressure) or raise the temperature.
To solve that question of yours, you must choose the option which gives you the weakest IMF. That option would exhibit the most ideal gas behaviour out of all the possible choices.
Hope it helps. Cheers.