At $S.T.P.$,if the compressibility factor $(Z)$ of a gas is less than $1$,then which of the following is true?

Identify the correct variation of pressure $(p)$ and volume $(V)$ of a real gas $(A)$ and an ideal gas $(B)$ at constant temperature. ($y = p$; $x = V$)

The deviation will be maximum in the behaviour of a gas from the ideal gas equation $PV = nRT$?

Under which conditions does the $van \ der \ Waals$ equation reduce to the ideal gas equation?

Calculate the compressibility factor $Z$ for $CO_2$,if one mole of it occupies $0.4 \ L$ at $300 \ K$ and $40 \ atm$. Also,comment on the result.

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 $dm^3$?