The triple point of a substance is:

The triple point of a substance is a specific condition where it can coexist in all three phases: solid, liquid, and vapor. This unique point occurs at a certain temperature and pressure, which is specific to each substance. At the triple point, any slight change in temperature or pressure can lead to a transition of the substance from one state to another, illustrating the dynamic equilibrium between the phases.

For example, water reaches its triple point at about 0.01 °C (273.16 K) and 611.657 pascals of pressure. At this precise combination of temperature and pressure, ice (solid), water (liquid), and water vapor (gas) exist simultaneously. This phenomenon is critical in thermodynamics and understanding phase diagrams, as it provides insight into the phase behavior of substances under varying conditions.

The other choices do not represent the definition of the triple point accurately. The point of maximum pressure does not indicate the coexistence of phases, and the minimum temperature does not specifically relate to phase coexistence. Additionally, the boiling point refers to the transition from liquid to vapor, without the presence of the solid phase. Thus, the definition correctly aligning with the concept of the triple point is the condition where a substance can exist as a