This point is the upper limit of the vapor-pressure line.

This point is the upper limit of the vapor-pressure line.

• A. Triple Point
• B. Critical Point
• C. Boiling Point
• D. Saturation Point

Answer: (B)

The point where the liquid–vapor boundary ends is the critical point. On a phase diagram, the vapor-pressure line shows the equilibrium between liquid and its vapor. As temperature rises, this boundary vanishes at the critical point, where liquid and vapor become indistinguishable and a supercritical fluid forms. That’s why it marks the upper limit of the vapor-pressure line. The triple point is where solid, liquid, and gas coexist, a separate feature lower on the diagram. The boiling point is the temperature at which a liquid’s vapor pressure equals the external pressure, not the endpoint of the liquid–vapor boundary. Saturation point isn’t the standard term for this endpoint.

The point where the liquid–vapor boundary ends is the critical point. On a phase diagram, the vapor-pressure line shows the equilibrium between liquid and its vapor. As temperature rises, this boundary vanishes at the critical point, where liquid and vapor become indistinguishable and a supercritical fluid forms. That’s why it marks the upper limit of the vapor-pressure line.

The triple point is where solid, liquid, and gas coexist, a separate feature lower on the diagram. The boiling point is the temperature at which a liquid’s vapor pressure equals the external pressure, not the endpoint of the liquid–vapor boundary. Saturation point isn’t the standard term for this endpoint.