$A$ real gas cannot be liquefied in which of the following conditions?

Explain how liquefaction can occur in different steps within the same phase using an example.

What are the critical constants?

Isotherms of carbon dioxide at various temperatures are represented in the figure. Answer the following questions based on this figure.
$(i)$ In which state will $CO_2$ exist between the points $a$ and $b$ at temperature $T_1$?
$(ii)$ At what point will $CO_2$ start liquefying when temperature is $T_1$?
$(iii)$ At what point will $CO_2$ be completely liquefied when temperature is $T_2$?
$(iv)$ Will condensation take place when the temperature is $T_3$?
$(v)$ What portion of the isotherm at $T_1$ represents liquid and gaseous $CO_2$ at equilibrium?

Which of the following conditions is most favorable for the liquefaction of a gas?

What is the surface tension at the critical temperature?