Question

Critical temperature and critical pressure values of four gases are given

Gas	C. Temp(K)	C.pressure(atm)
P	5.1	2.2
Q	33	13
R	126	34
S	135	40

Which of the gas/gases cannot be liquefied at a temperature of 100 K and a pressure of 50 atmospheres?

• A. S only
• B. P only
• C. R and S
• D. P and Q

Answer 1

The correct option is D P and Q

Gases cannot be liquefied above the critical temperature however high the pressure may be applied. Because, above the critical temperature, molecules will have a large amount of kinetic energy which will be sufficient enough to overcome the intermolecular force of attraction.
As P and Q gases have a critical temperature less than $100K$ whereas, R and S have critical temprature higher than $100K$, therefore P and Q gases cannot be liquified at a temperature $100K$ and $50atm$.