Liquefaction of Gases — Prelims Questions

Which of the following statements about the critical temperature ($T_c$) of a gas is INCORRECT?

For a gas to show a cooling effect upon adiabatic expansion (Joule-Thomson effect), its temperature must be:

Given the critical temperatures for four gases: $ext{NH}_3 (405.5 \text{ K})$, $ext{CO}_2 (304.1 \text{ K})$, $ext{O}_2 (154.6 \text{ K})$, $ext{He} (5.2 \text{ K})$. Arrange them in increasing order of ease of liquefaction.

According to Andrews' experiments on $ext{CO}_2$, what happens in the horizontal portion of an isotherm below the critical temperature?

Which of the following gases would be most difficult to liquefy?

Which of the following factors primarily contributes to the cooling observed in the Joule-Thomson effect for most gases?