For which of the following is the van der Waals equation valid?

Pressure versus volume graph for a real gas and an ideal gas are shown in the figure. Answer the following questions on the basis of this graph:
$(i)$ Interpret the behaviour of real gas with respect to ideal gas at low pressure.
$(ii)$ Interpret the behaviour of real gas with respect to ideal gas at high pressure.
$(iii)$ Mark the pressure and volume by drawing a line at the point where real gas behaves as an ideal gas.

The $P$ vs $V$ graph is plotted for $1$ $mole$ of a hypothetical gas. Based on the given isotherms at $200 \ K$ and $300 \ K$,determine the range of $\frac{a}{b}$ for this gas in $atm-L \ mole^{-1}$. [Given: $R = 0.08 \ atm-L \ mole^{-1} \ K^{-1}$]

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

At low pressures,van der Waals' equation is written as $(P + \frac{a}{V^2})V = RT$. The compressibility factor $Z$ will be

When is deviation more in the behaviour of a gas from the ideal gas equation $PV = nRT$?