For an ideal gas, Z = 1 at any temperature or pressure.

Boyle point depends on the nature of the real gas. Above the Boyle point Z is greater than 1.

At low pressures and high temperatures muchabove the critical point of the substance, the real gases can be taken to behave like ideal gases. Gases like O₂, N₂,H₂, He, mono-atomic gases and inert gases behave NEARLY ideal at standard temperature (0⁰C) and pressure (1 standardatmosphere).

Ideal gas law does not take into account the molecular size, andinter-molecular attraction or repulsion forces. It assumes that those factors are zero. In mono-atomic gases this assumption is valid over a wide range of pressures and temperatures. But in otherreal gases, inter-molecular forces are weak at high temperatures and low pressures. The reason is high kinetic energy overcomes small inter-molecular forces as the molecules are separated by large distances. The moleculesoccupyvery little space compared to the totalvolume of the gas.

define temperature .