Which gas among the following is the easiest to liquify?

At $S.T.P.$,if the compressibility factor $(Z)$ of a gas is less than $1$,then which of the following is true?

The pressure exerted by $5 \, mol$ of a real gas in a $1 \, L$ container at $47 \, ^oC$ is ............. $atm$. $\left( a = 3.592 \, atm \, L^2 \, mol^{-2}, b = 0.0427 \, L \, mol^{-1} \right)$

$A$ certain gas obeys $P(V_{m}-b)=RT$. The value of $(\frac{\partial Z}{\partial P})_{T}$ is $\frac{xb}{RT}$. The value of $x$ is .... .
(Integer answer) ($Z$: compressibility factor)

Consider the equation $Z = \frac{PV}{RT}.$ Which of the following statements is correct?

Gases deviate from ideal behaviour at high pressures because the gas molecules