Here is the full MCQ from CIE....
Measured values of the pressure, volume and temperatureof a
known mass of a gaseous compound are to be susbstituted into the
equation
Pv= nRT
In order to calculate the relative molecular mass of the
compound
Which conditions of pressure and temperature would give the most
accurate valuesof Mr?
pressure
temperature
A
high
high
B
high
low
C
low
high
D
low
low
For this particular MCQ, the answer is C, because the behavior of
gases approach ideal gas behavior most closely at high temperatures
and low pressures. PV=nRT only holds true for ideal gases, not real
gases.