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

Real gases show deviation from ideal gas behavior because the molecules .............

The variation of the compressibility factor $(Z)$ with pressure $(P$ in $bar)$ for some gases is shown in the figure below. Identify the gases $(A)$, $(B)$, and $(C)$.

When does the graph of $p \propto \frac{1}{V}$ not result in a straight line?

Which of the following represents the Van der Waals equation for $n$ moles of a gas?

For real gases,the relation between $p$,$V$,and $T$ is given by the van der Waals equation:
$(p + \frac{an^2}{V^2})(V - nb) = nRT$
Where $a$ and $b$ are van der Waals constants,$nb$ is approximately equal to the total volume of the molecules of a gas,and $a$ is the measure of the magnitude of intermolecular attraction.
$(i)$ Arrange the following gases in the increasing order of $b$. Give reason: $O_2, CO_2, H_2, He$
$(ii)$ Arrange the following gases in the decreasing order of magnitude of $a$. Give reason: $CH_4, O_2, H_2$