Question: Which of the following statements is true regarding the phase diagram of a substance?

Options:

1. The triple point is where all three phases coexist
2. The critical point is where the solid and liquid phases coexist
3. The vapor pressure curve separates solid and liquid phases
4. The solid phase is always more stable than the liquid phase

Correct Answer: The triple point is where all three phases coexist

Solution:

The triple point on a phase diagram is the unique set of conditions at which all three phases (solid, liquid, gas) coexist in equilibrium.