The point on a phase diagram where all three phases in equilibrium is called the

• A. Critical Point
• B. Phase Diagram
• C. Triple Point
• D. Phase Boundaries

Answer: (C)

This is about the condition where solid, liquid, and gas coexist in equilibrium for a substance. The point where all three phases are in balance is the triple point. It is a specific temperature and pressure unique to each material; for water, it occurs at about 0.01°C and roughly 611 pascals (0.006 atm).

The other terms describe different ideas on a phase diagram: the critical point is where liquid and gas become indistinguishable and form a supercritical fluid; the phase diagram is the map itself; phase boundaries are the lines that separate one phase from another on that map. The triple point is the intersection where the three phase boundaries meet, signifying coexistence of all three phases.