A supercritical fluid extraction solvent is picked mainly for having a critical temperature close to room temperature, so heat-sensitive drug compounds are not damaged during extraction. Carbon dioxide fits this need better than almost any other common solvent, which is why its exact critical point matters here.
- 34°C and 50 atm: The temperature is near CO2's actual value, but the pressure quoted is noticeably lower than CO2 truly needs to reach its supercritical state, so it does not fit.
- 31.1°C and 73.8 atm: Carbon dioxide becomes supercritical once it passes 31.1°C and 73.8 atm at the same time. Below either value it stays a liquid or gas; only past both does it show the dense, gas-like diffusing solvent behavior extraction depends on.
- 54°C and 78 atm: A temperature this high would require far more heating than CO2 actually needs, making it unsuitable as a description of CO2's critical point.
- 40°C and 60 atm: This combination is a rough guess that does not match any standard reference value for CO2.
The pair that matches published critical constant tables for carbon dioxide is the second option.
So the correct answer is 31.1°C and 73.8 atm.