In this answer I've asserted (without a "Chemist's license") that as long as oxygen is above it's critical point in both temperature (154.5 K) and pressure (50.4 bar) it's going to be a supercritical fluid.
This comment by a user who I believe is an experienced diver says:
Scuba divers use the idea(l) gas law for air and oxygen bottles to calculate the amount of remaining gas for 200 down to 10 bar. This would not be possible if there is supercritical oxygen in the tank.
In other words, the ideal gas law works pretty well for oxygen between 10 and 200 bar; for a given temperature the amount of oxygen (number of atoms or mass in kg) is close to linearly proportional to pressure.
The comment proposes that this is evidence that the oxygen couldn't be a supercritical fluid.
- When oxygen is above both 50.4 bar and 154.5 K is it always a supercritical fluid, end of story?
- If it is, would it nonetheless still tend to follow fairly closely the ideal gas law?