Answer:
Ideal?
Explanation:
This question is lacking context, but it's most likely looking for ideal. There is an idea of "ideal" gasses, which are gasses the behave according the ideal gas law PV=nRT. The concept is the gasses can get very close to behaving ideally, but there is never a gas the will perfectly obey the ideal gas law. There are many factors that affect this, but I won't get into thoes since that's not what the question asked.
