Which of the following gases is most difficult to liquefy?

$A$ gas can be liquefied at temperature $T$ and pressure $p$ provided:

Which among the following gases is difficult to liquefy?

Two different gases $A$ and $B$ are filled in separate containers of equal capacity under the same conditions of temperature and pressure. On increasing the pressure slightly,gas $A$ liquefies,but gas $B$ does not liquefy even on applying high pressure until it is cooled. Explain this phenomenon.

What are the most favourable conditions to liquefy a gas?

Which intermolecular force is most responsible for allowing $Xe$ gas to liquefy?