Saturated vapor, sensible heat, and phase-diagram endpoints:\nWhich statement is correct regarding saturation and phase-equilibrium curves?

Introduction / Context:
Understanding terminology around saturation, sensible/latent heat, and phase diagrams is fundamental in thermodynamics and process design. Misusing these terms leads to incorrect assessments of condensation, boiling, and energy duties in heat exchangers and separation equipment.

Given Data / Assumptions:

• Pure-substance phase diagram behavior.
• Standard definitions of sensible and latent heat.
• Saturated states defined by equality of partial and saturation pressures at a given temperature.

Concept / Approach:
The vapor-pressure curve (liquid–vapor equilibrium line) of a pure substance spans from the triple point (where solid, liquid, and vapor coexist) to the critical point (where liquid and vapor become indistinguishable). A saturated vapor exists on this line below the critical temperature; above the critical temperature, no saturation state exists—only supercritical fluid/gas. Sensible heat refers to heat causing temperature change; latent heat refers to heat added or removed at constant temperature during a phase change at equilibrium.

Step-by-Step Solution:

Verification / Alternative check:
Consult any standard phase diagram; the liquid–vapor line indeed ends at the triple and critical points.

Why Other Options Are Wrong:

• (a) Mislabels supercritical or superheated states as “saturated.”
• (b) Misstates the saturation condition; equality, not “exceeds,” defines saturation.
• (c) Confuses sensible with latent heat.

Common Pitfalls:
Interchanging dew/bubble/saturation conditions; calling any constant-temperature heat exchange “sensible.”

Final Answer:
The vapor-pressure vs. temperature curve of a pure substance terminates at the triple point and the critical point.