The cooling in a refrigerator is due to

For the following gases,the values of $'a'$ (van der Waals constant) are given in parentheses: $CH_4 (2.25)$,$N_2 (1.35)$,$O_2 (1.36)$,and $CO (1.46)$. Which gas will be the most difficult to liquefy?

$A$ gas has a compressibility factor of $0.5$ and a molar volume of $0.4 \ dm^3 \ mol^{-1}$ at a temperature of $800 \ K$ and pressure $x \ atm$. If it shows ideal gas behaviour at the same temperature and pressure,the molar volume will be $y \ dm^3 \ mol^{-1}$. The value of $x / y$ is . . . . . .
[Use: Gas constant,$R = 8 \times 10^{-2} \ L \ atm \ K^{-1} \ mol^{-1}$ ]

In the given $pV \to V$ graph for gases at constant temperature,what kind of deviation will be observed for $H_2, He, CO, CH_4$?

Identify the wrong relation for real gases :

At $300 \, K$ temperature and $40 \, atm$ pressure,if one mole of $CO_2$ occupies $0.4 \, L$,then it is: