For real gases following van der Waal's equation of state, at critical temperature, liquid phase and vapour phase have the same densities, as there is no distinction between liquid state and vapour phase.
Also at critical temperature, the terms [∂P∂V]T and [∂2P∂V2]T are equal to zero.
At critical temperature, the value of the compressibility factor z is equal to 38. Real gases are more compressible than ideal gases. This is because the value of z is less than 1 and the real gas occupies lesser volume than ideal gas.