Final answer:
The triple point is the condition at which a substance exists in equilibrium as a solid, liquid, and gas. The boiling point and freezing point are states of equilibrium between a liquid and a gas, and a liquid and a solid, respectively.
Step-by-step explanation:
The triple point of a gas is the pressure and temperature at which a substance exists in equilibrium as a solid, liquid, and gas. It is the one condition where all three phases coexist at equilibrium. The triple point can be identified from the phase diagram as the point where all three curves intersect.
The state of equilibrium between a liquid and a gas is known as the boiling point. It is the temperature at which the vapor pressure of the liquid equals the atmospheric pressure. The state of equilibrium between a liquid and a solid is known as the freezing point. It is the temperature at which the liquid solidifies into a solid. The state of equilibrium between a gas and a solid is not commonly encountered, but it can exist under certain conditions.