Under what conditions do real gases behave as ideal gases?

$A$ gas described by van der Waal's equation:

$A$ gas deviates from ideal behaviour at a high pressure because its molecules

One of the assumptions of the kinetic theory of gases is that there is no force of attraction between the molecules of a gas. State and explain the evidence that shows that this assumption is not applicable for real gases.

Calculate the compressibility factor for $SO_2$,if $1 \ mol$ of it occupies $0.35 \ L$ at $300 \ K$ and $50 \ atm$ pressure.

The correct equation for one mole of a real gas is ($a, b$ are constants)