(i). Variation of volume of the gas sample with temperature at constant pressure.
(ii). Each line (iso bar) represents the variation of volume with temperature at certain pressure. The pressure increases from P1 to P5 .
(iii). i.e. P1 < P2 < P3 < P4 < P5. When these lines are extrapolated to zero volume, they intersect at a temperature of -273.15°C.
(iv). All gases are becoming liquids, if they are cooled to sufficiently low temperatures.
(v). In other words, all gases occupy zero volume at absolute zero. So the volume of a gas can be measured over only a limited temperature range.