$A$ gas can be liquefied:

Explain the liquefaction of real gases and permanent gases.

What is the surface tension at the critical temperature?

$A$ liquid can exist only,

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?

Distinguish between vapor and gas.