What information does a phase diagram provide about a substance?

A phase diagram is a graphical representation that illustrates the states of a substance (solid, liquid, gas) as they change with variations in temperature and pressure. The axes typically consist of temperature along one axis and pressure along the other, enabling one to identify the conditions under which specific phases are stable.

When analyzing a phase diagram, one can observe phase boundaries that indicate transitions, such as melting (solid to liquid) and boiling (liquid to gas). Inside the regions of the diagram, you can determine what state the substance will be in at any given combination of temperature and pressure. This is crucial for understanding material behavior in different environmental conditions, which can be applied in numerous scientific and engineering fields.

Thus, the phase diagram effectively communicates the relationships between temperature, pressure, and the physical states of a substance, making option C the correct choice.