Point D on the phase diagram is known as the critical point.
The critical point on a phase diagram, like Point D, represents the highest temperature and pressure at which a substance can exist in phase equilibrium.
At this point, the substance is a supercritical fluid, a state where it’s indistinguishable as a liquid or gas.
The critical point in a phase diagram is a unique state at which the distinction between liquid and gas phases ceases to exist. It’s the end of the phase equilibrium curve, defined by a critical pressure (Pc) and critical temperature (Tc).