Define triple point of a substance. Write its value of temperature and pressure for water.

Explanation

### Step-by-Step Solution

**Step 1: Define the Triple Point of a Substance**
The triple point of a substance is defined as the specific temperature and pressure at which the three phases of that substance—solid, liquid, and vapor—coexist in thermodynamic equilibrium. At this point, all three phases can exist simultaneously without any phase transitioning into another.

**Step 2: Explain the Concept of Equilibrium**
At the triple point, the solid, liquid, and vapor phases are in equilibrium, meaning that the rates of phase transitions (melting, freezing, vaporization, and condensation) are balanced. This equilibrium is represented graphically by the intersection of the fusion curve, vaporization curve, and sublimation curve on a phase diagram.

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