The phase of water at 0.5 atm and 100°C is gaseous phase.
Water exists in three different phases such as liquid, gas, and solid.
The phase of the given water can be determined using phase diagram at standard temperature and pressure as shown in the image uploaded.
At 0.5 atm and 100 °C, the water is still in vapour or gaseous phase.
Thus, the phase of water at 0.5 atm and 100°C is gaseous phase.
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