Maximum deviation from ideal gas behavior is expected from which of the following gases?

Which of the following formulae is used to determine the compressibility factor $(Z)$ for the measurement of deviation from ideal behavior?

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)

The relation between pressure exerted by an ideal gas $(P_{ideal})$ and observed pressure $(P_{real})$ is given by the equation
$P_{ideal} = P_{real} + \frac{an^2}{V^2}$
$(i)$ If pressure is taken in $N \ m^{-2}$,number of moles in $mol$,and volume in $m^3$,calculate the unit of $a$.
$(ii)$ What will be the unit of $a$ when pressure is in atmosphere and volume in $dm^3$?

Excluded volume $(v)$ per molecule is related to the van der Waals constant $'b'$ in the following way:

$CH_4$ gas is behaving non-ideally. The compressibility factor for the gas is $1.5$ at $2 \ atm$ and $400 \ K$. Calculate the molar volume for the gas in $litre$. [Given $R = 0.08 \ L \ atm \ K^{-1} \ mol^{-1}$]