Final answer:
It is important for water to be free of air because air can interfere with the accurate determination of the triple point temperature.
Step-by-step explanation:
The triple point of air-free water is defined as 273.16 K. It is important for the water to be free of air because air can interfere with the accurate determination of the triple point temperature. The triple point temperature is a more accurate calibration temperature than the freezing point of water, which depends on factors such as the amount of dissolved air and atmospheric pressure.