The van der Waals equation reduces to the ideal gas equation under which of the following conditions?

Which of the given sets of temperature and pressure will cause a gas to exhibit the greatest deviation from ideal gas behavior?

What is the reason for the deviation of pressure from ideal behavior?

The compressibility factor of a gas is less than $1$ at $STP$. Its molar volume $V_m$ will be

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: $CH_4, O_2, H_2$

For a gas at $STP$,the compressibility factor is greater than $1$. What will be the value of its molar volume $(V_m)$?