Assertion : At critical point the densities of substance in gaseous...

Temperature at which the real gas exhibit ideal behaviour for considerable range of pressure is known as Boyle's temperature. $T_b=\frac{a}{b R} a$, and $b$ are van der Waal's constant. Critical temperature is the temperature above which the gas cannot be liquefied, how so ever high pressure may be applied : $T_c=\frac{8 a}{27 R b}$.