At low pressure,the van der Waals equation becomes

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 $dm^3$?

In the $Vander$ $Waals$ equation,the constant $'b'$ is a measure of $......$.

If the compressibility factor $(Z)$ of a gas at $STP$ is greater than $1$,then what will be the value of its molar volume $(V_m)$?

In the van der Waals equation,which of the following will have the highest value of '$a$'?

$A$ real gas would be most likely to obey the ideal gas laws at