Final answer:
A mass of 5 kg of saturated water vapor represents a gas (B). This gas is at a specific temperature and pressure where it can exist in equilibrium with its liquid phase. At very low pressures, water may not have a liquid phase and can undergo sublimation, directly transitioning from solid to gas.
Step-by-step explanation:
When we refer to 5 kg of saturated water vapor, we're talking about water in the gas phase at a temperature where it is about to condense into the liquid phase, or conversely, the liquid is at the point of becoming vapor. This means that it represents a gas, not a liquid (answer B). Saturated vapor is at a specific temperature and pressure where it exists in equilibrium with its liquid phase; it contains no impurities in the context of this definition (which eliminates answer C), and it does not imply that the water vapor is at the freezing point (which eliminates answer D).
The concept of water having different states based on temperature and pressure is essential in understanding phase changes. At very low pressures, such as below 0.00600 atm for water, there is no liquid phase. Sublimation occurs at this point, which is a phase change from solid to gas without going through the liquid phase. Conversely, under different conditions, water may exist as a liquid or solid—a versatility that defines its phase behaviour.