What conclusion would you draw from the following graphs for an ideal gas?

An open-ended mercury manometer is used to measure the pressure exerted by a trapped gas as shown in the figure. Initially, manometer shows no difference in mercury level in both columns as shown in the diagram. After sparking $"\mathrm{A}"$ dissociates according to the following reaction $\mathrm{A} \left(\mathrm{g}\right)⟶\mathrm{B} \left(\mathrm{g}\right)+3\mathrm{C} \left(\mathrm{g}\right).$

If pressure of Gas $"\mathrm{A}"$ decreases to $0.9 \mathrm{atm}.$ 
(Assume temperature to be constant and is $300 \mathrm{K}$)

Which of the following is/are correct?

Which of following statement (s) is(are) true

$\mathrm{I}$- The slope of isotherm at the critical point is maximum.

$\mathrm{II}$-Larger is the value of $\mathrm{Tc}$, easier is the liquification of gas.

$\mathrm{III}$-Vander waal's equation of state is applicable below critical temperature at all pressure.

Consider the following statements: If the Van der Waals parameters of two gases are given as:

Then$\left(\mathrm{i}\right): {\mathrm{V}}_{\mathrm{c}} \left(\mathrm{X}\right) < {\mathrm{V}}_{\mathrm{c}} \left(\stackrel{}{\mathrm{Y}}\right)$ (ii)$:Pc \left(\mathrm{X}\right) <Pc \left(\mathrm{Y}\right)$
(iii): $Tc \left(\mathrm{X}\right)<Tc \left(\mathrm{Y}\right)$
Select the correct statement.