Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases.

$Gases$	$H_2$	$He$	$O_2$	$N_2$
$Critical \ temperature \ (K)$	$33.2$	$5.3$	$154.3$	$126$

From the above data,what would be the decreasing order of liquefaction of these gases?

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?

Critical constants for a real gas are given as:
$T_C = 180 \ K$; $V_C = 0.123 \ L \ mol^{-1}$
$P_C = 45 \ atm$; $R = 0.082 \ L \ atm \ mol^{-1} \ K^{-1}$
Which of the following statements is correct for this real gas?

For gases $W, X, Y$ and $Z$,the van der Waals constants are given below. Which gas has the highest critical temperature?

Gas	$a$ (atm $L^2$ mol$^{-2}$)	$b$ ($L$ mol$^{-1}$)
$W$	$4.0$	$0.027$
$X$	$8.0$	$0.030$
$Y$	$6.0$	$0.032$
$Z$	$12.0$	$0.027$

What are the critical constants?

$A$ liquid can exist only,