What will the van der Waals equation be at high temperature and low pressure?

The Van der Waals constants '$a$' and '$b$' are related to which of the following respectively?

The correct increasing order of the value of van der Waals's constant $a$ for $CH_4, O_2$ and $H_2$ gases is

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 $(C)$.

Define the compressibility factor $(Z)$ in terms of the molar volume of a gas.

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.