Question

An ideal gas obeying kinetic theory of gases can be liquefied if:

• A. Its temperature is more than critical temperature $T_c$
• B. Its pressure is more than critical pressure $P_c$
• C. Its pressure is more than $P_c$ at a temperature less than $T_c$
• D. It cannot be liquefied at any value of P and T

Answer 1

The correct option is D It cannot be liquefied at any value of P and T

An ideal gas cannot be liquefied at any value of $P$ and $T$ since there are no intermolecular interactions between molecules.
Such a system can only exist as a gas. Any real system will approach ideal gas behavior in the limit that the pressure is extremely low and the temperature is high enough to overcome attractive intermolecular forces.
An ideal gas has no forces of attraction and has negligible volume. Hence, it cannot be liquefied at any T and P.
So, the correct option is $\left(d\right)$.