Final answer:
The critical point on a phase diagram represents conditions where a substance's liquid and gas phases become indistinguishable; for water, it's 373.99° C and 217.75 atm, and for CO₂, it's at 30.98° C and 72.79 atm.
Step-by-step explanation:
The function mentioned refers to the physical behavior of a substance on its phase diagram, where the critical point is a specific set of conditions. At the critical point, specifically pertaining to water, the critical temperature (Tc) is 373.99° C, and the critical pressure (Pc) is 217.75 atm. This is the temperature and pressure above which water's liquid and gas phases become indistinguishable.
For carbon dioxide (CO₂), the critical point occurs at 30.98 degrees C and 72.79 atm. The critical point indicates that no matter how much pressure is applied, a gas cannot be liquefied above its critical temperature because the kinetic energy of the particles is too great for intermolecular forces to condense it into a liquid.