Distinguish between vapor and gas.

Explain the liquefaction of real gases and permanent gases.

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

$Gases$	$H_2$	$He$	$O_2$	$N_2$
$Critical \ temperature \ (K)$	$33.2$	$5.3$	$154.3$	$126$

From the above data,what would be the decreasing order of liquefaction of these gases?

Which among the following gases liquefy easily?

What is the temperature below which a gas cannot exist as a gas (i.e.,it liquefies) called?

Which of the following gases is most difficult to liquefy?