Which set of conditions represents the easiest way to liquefy a gas?

At what pressure does $SO_2$ gas liquefy at room temperature?

Under what conditions can an ideal gas,which follows the kinetic gas equation,be liquefied?

However great the pressure,a gas cannot be liquefied above its

Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases:

$Gases$	$Critical \ temperature \ in \ Kelvin$
$P$	$33.2$
$Q$	$5.3$
$R$	$154.3$
$S$	$126$

From the above data,what would be the order of liquefaction of these gases? Start writing the order from the gas liquefying first.

Which among the following gases liquefy easily?