Final answer:
The conditions under which H₂O can exist include liquid water and water vapor at 25 °C with a 0.03 atm pressure, or as a supercritical fluid. Other experiments involve transforming water to gas and back to liquid for mass measurement, along with an example of gas distribution in a vacuum.
Step-by-step explanation:
The question relates to the phase of water (H₂O) under different conditions. When we have a sealed container of water at 25 °C and remove the air, we allow the water to establish a vaporization-condensation equilibrium, resulting in a mixture of liquid water and water vapor at a pressure of 0.03 atm. At this state, we can see a clear boundary between the dense liquid and the less dense gas. However, if we increase the temperature and pressure beyond the critical point of water, we get a supercritical fluid where this distinction disappears.
Another experiment involves heating a flask to turn liquid water to gas and then removing the flask from heat as the last bit of liquid converts to gas, leaving a flask filled with gaseous water. A third condition is sealing the flask and allowing the gas to condense back to liquid for weighing, which permits the determination of the sample's mass.
The question also mentions scenarios like a second flask containing a vacuum, where upon opening a valve between it and a flask of gas, the gas will spread evenly between the two flasks. An experiment proposed suggests getting three buckets of water: room temperature, very hot, and very cold (with ice), which deals with the sensory experience of water at different temperatures but does not seem directly related to the scientific behavior of water's phases under varying conditions.