Correct Answer: C
Explanation:
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. For example, the triple point of mercury occurs at a temperature of −38.83440 oC and a pressure of 0.2 mPa.
The triple point of water is used to define the kelvin, the base unit of thermodynamic temperature in the International System of Units (SI). The value of the triple point of water is fixed by definition, rather than measured. The triple point of water 32.018oF (273.16 K, or 0.01 oC).