Question

(b) A gas can be liquefied, when
(i) T>T; P = Pc
(i) T < T; P < PC
(ii) T < T; P > Pa
(iv) T = Tc; P < Pc​

Answer 1

iv) T = Tc ; P < Pc is correct

This is because after critical temperature and critical pressure, no gas can be liquefied. Therefore, Temperature and pressure should be either equal to or less than critical temperature and critical pressure respectively.

Hope it helps !