Answer:
pressure
Explanation:
The phase diagram is a graph used to indicate the temperature and pressure conditions necessary to obtain a substance in a specific physical state (solid, liquid or gas). In this type of diagram, pressure is a factor that is kept constant.
The x (horizontal) axis contains the temperature values, and the y (vertical) axis contains the pressure values. In addition, there are three curves connected to a single point (called a triple point), dividing the graph into three well-defined areas, as we can see in the diagram shown above.
In addition to indicating the conditions for the substance to be in a specific physical state, the phase diagram indicates the conditions for any change in physical state to occur.
