The critical point of this substance occurs at what temperature?

• A. 0 °C
• B. –78.5 °C
• C. –56.7 °C
• D. 31 °C
• E. 100 °C

Answer: (D)

Verified step by step guidance

1. Identify the critical point on the phase diagram, which is the point where the liquid and gas phases become indistinguishable.
2. Locate the critical point on the diagram, which is marked by the end of the liquid-gas boundary curve.
3. Read the temperature value corresponding to this critical point on the x-axis of the phase diagram.
4. Note that the critical point temperature is where the pressure is 72.9 atm and the temperature is 31 °C.
5. Conclude that the critical temperature of the substance is 31 °C based on the phase diagram.