Gases deviate from the ideal gas behaviour because their molecules

$A$ gas has a compressibility factor of $0.5$ and a molar volume of $0.4 \ dm^3 \ mol^{-1}$ at a temperature of $800 \ K$ and pressure $x \ atm$. If it shows ideal gas behaviour at the same temperature and pressure,the molar volume will be $y \ dm^3 \ mol^{-1}$. The value of $x / y$ is . . . . . .
[Use: Gas constant,$R = 8 \times 10^{-2} \ L \ atm \ K^{-1} \ mol^{-1}$ ]

Under which conditions does a gas show the greatest deviation from the ideal gas equation $PV = nRT$?

At relatively high pressure,the van der Waals equation becomes?

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

In the following compressibility factor $(Z)$ versus pressure graph at $300 \, K$,the compressibility of $CH_{4}$ at pressure $< 200 \, bar$ deviates from ideal behaviour because