$\mathbf{Q:}$ While teaching "Real Gases", my professor remarked last day that "Liquid phase is a highly compressed gaseous phase." But he did not explain the reason behind it and left it as food for our thought.
$\mathbf{A:}$ What I could make out of this was that he was referring to the isotherms of real gases. So I got this graph.
Now I can see from the graph that a certain finite amount of pressure needs to be applied in order that we can change the gaseous state from vapor to liquid. Ideal gases have considerable or high compressibility while ideal liquids are almost incompressible. But still can I call this "highly compressed"? So how do I prove the statement made by my professor?
Any help in the form of hints or answers is welcome.