Which among the following gases liquefy easily?

$A, B, C$ and $D$ are four different gases with critical temperatures $304.1, 154.3, 405.5$ and $126.0 \ K$ respectively. While cooling the gas,which gets liquefied first?

Which among the following gases is difficult to liquefy?

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:

$A$ gas can be liquefied at temperature $T$ and pressure $p$ provided:

For gases $W, X, Y$ and $Z$,the van der Waals constants are given below. Which gas has the highest critical temperature?

Gas	$a$ (atm $L^2$ mol$^{-2}$)	$b$ ($L$ mol$^{-1}$)
$W$	$4.0$	$0.027$
$X$	$8.0$	$0.030$
$Y$	$6.0$	$0.032$
$Z$	$12.0$	$0.027$