Which of the following best describes the triple point of water?

• A. The pressure at which water boils at 100 °C.
• B. The temperature and pressure at which ice melts into liquid water.
• C. The temperature and pressure at which water can exist simultaneously as a solid, liquid, and gas in equilibrium.
• D. The temperature at which water freezes at standard atmospheric pressure.

Answer: (C)

Verified step by step guidance

1. Understand that the triple point of a substance is a unique condition where three phases coexist in equilibrium.
2. Recall that for water, the three phases are solid (ice), liquid (water), and gas (water vapor).
3. Recognize that the triple point is defined by a specific temperature and pressure where all three phases are stable together.
4. Note that this is different from boiling point or melting point, which involve only two phases in equilibrium.
5. Conclude that the triple point of water is the temperature and pressure at which ice, liquid water, and water vapor coexist simultaneously in equilibrium.