What are the most favourable conditions to liquefy a gas?

The temperature below which a gas cannot exist is called ...............

The liquified gas that is used in dry cleaning along with a suitable detergent is

What is the value of the critical temperature of water (in $K$)?

$A, B, C$ and $D$ are four different gases with critical temperatures $304.1, 154.3, 405.5$ and $126.0 \ K$ respectively. While cooling the gas,which gets liquefied first?

Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the gas particles. Critical temperatures of ammonia and carbon dioxide are $405.5 \ K$ and $304.10 \ K$ respectively. Which of these gases will liquefy first when you start cooling from $500 \ K$ to their critical temperature?