$A$ real gas cannot be liquefied in which of the following conditions?

The compressibility factor $(Z)$ of a gas at critical state is $(T_c = \frac{8 a}{27 R b}; p_c = \frac{a}{27 b^2}; V_c = 3 b)$.

The isotherms of a gas are shown below:
Among the following:
$(i)$ At $T_1$,the gas cannot be liquefied.
$(ii)$ At point $B$,liquid starts to appear at $T_2$.
$(iii)$ $T_c$ is the highest temperature at which the gas can be liquefied.
$(iv)$ At point $A$,a small increase in pressure condenses the whole system to a liquid.
The correct statements are:

Assertion : At critical temperature,liquid passes into gaseous state imperceptibly and continuously.
Reason : The density of liquid and gaseous phase is equal at critical temperature.

Which of the following gases has the highest critical temperature?

Liquefaction of a gas can occur $....................$