Which of the following regions on a phase diagram represents the coexistence of both liquid and gas phases?

• A. The area labeled as 'liquid'
• B. The area labeled as 'solid'
• C. The line separating the liquid and gas regions (the liquid-gas equilibrium line)
• D. The area labeled as 'gas'

Answer: (C)

Verified step by step guidance

1. Understand that a phase diagram shows the state of a substance (solid, liquid, gas) at different temperatures and pressures.
2. Recognize that regions on the diagram represent single phases: 'solid', 'liquid', or 'gas'.
3. Identify that the coexistence of two phases occurs along the boundary lines between these regions, where the substance can exist in equilibrium between those phases.
4. Focus on the line separating the liquid and gas regions, which is called the liquid-gas equilibrium line or vaporization/condensation line.
5. Conclude that this line represents the coexistence of both liquid and gas phases, as the substance can transition between these two phases at points along this line.