What are the most favourable conditions to liquefy a gas?

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

The statement that is $NOT$ correct is

Assertion : At critical temperature,liquid passes into gaseous state imperceptibly and continuously.
Reason : The density of liquid and gaseous phase is equal at critical temperature.

The critical temperatures $(T_C)$ of some gases are given below:

Gases	$H_2, He, O_2$
$T_C \ (K)$	$33.2, 5.3, 154.3$

Based on the above data,what is the order of liquefaction of these gases? Start writing the order from the gas that liquefies first.

The critical temperature of $O_2$ is $154.3 \ K$ and the critical temperature of $N_2$ is $126.0 \ K$. Which gas will liquefy first during the liquefaction of air?