$A$ gas is said to behave like an ideal gas when the relation $PV/T = \text{constant}$. When do you expect a real gas to behave like an ideal gas?

What is the volume of $1 \ mole$ of a real gas at $STP$ $(V_{ideal} = 22.4 \ dm^3)$,if the compressibility factor of the real gas is $1.1$ at $STP$ (in $dm^3$)?

The unit of the Van der Waals constant '$a$' is .......

At high pressure,the form of 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 $dm^3$?

What is the correction term in the pressure for real gas in comparison to the ideal gas?