For which of the following gases will the van der Waals constant $'a'$ have the highest value?

What is the pressure of $2 \, mol$ of $NH_3$ at $27 \, ^oC$ when its volume is $5 \, L$ using the van der Waals equation (in $, atm$)? ($a = 4.17 \, L^2 \, bar \, mol^{-2}$,$b = 0.03711 \, L \, mol^{-1}$)

For $NH_3$ gas,the $Z$ vs pressure $(P)$ curve at different temperatures is shown. What is the correct order of temperatures? (Given $T_B$ = Boyle temperature)

Match the Van der Waals constant $a$ (in $L^2 \cdot bar \cdot mol^{-2}$) for the following gases:

Gas	$a$ value
$1. C_6H_{6(g)}$	$a. 0.217$
$2. C_6H_5CH_{3(g)}$	$b. 5.464$
$3. Ne_{(g)}$	$c. 18.000$
$4. H_2O_{(g)}$	$d. 24.060$

The pressure exerted by $5 \ mol$ of a real gas in a $1 \ L$ container at $47 \ ^oC$ is ......... $atm$. (Given: $a = 3.592 \ atm \ L^2 \ mol^{-2}$,$b = 0.0427 \ L \ mol^{-1}$)

The compressibility factor $(Z)$ of a gas is less than unity at $STP$,then: