$A$ gas behaves as an ideal gas under which of the following conditions?

$A$ plot of the compressibility factor $(z)$ vs $P$ is shown below for $H_2, He, N_2, CO_2$ and $SO_2$. Identify the plot for $CO_2$ gas.

$A$ gas has a compressibility factor of $0.5$ and a molar volume of $0.4 \ dm^3 \ mol^{-1}$ at a temperature of $800 \ K$ and pressure $x \ atm$. If it shows ideal gas behaviour at the same temperature and pressure,the molar volume will be $y \ dm^3 \ mol^{-1}$. The value of $x / y$ is . . . . . .
[Use: Gas constant,$R = 8 \times 10^{-2} \ L \ atm \ K^{-1} \ mol^{-1}$ ]

The Van der Waals parameters for gases $W$,$X$,$Y$,and $Z$ are given below. Which one of these gases has the highest critical temperature?

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

Consider the van der Waals constants,$a$ and $b$,for the following gases:

Gas	$Ar$	$Ne$	$Kr$	$Xe$
$a / (atm \ dm^6 \ mol^{-2})$	$1.3$	$0.2$	$5.1$	$4.1$
$b / (10^{-2} \ dm^3 \ mol^{-1})$	$3.2$	$1.7$	$1.0$	$5.0$

Which gas is expected to have the highest critical temperature?

For which of the following is the van der Waals equation valid?