Answer:
Water at 100°C and 500 kPa is in the liquid phase.
Step-by-step explanation:
We can determine the phase of a substance at a determinate temperature and pressure by looking at its phase diagram. We have to find the intersection of the pressure (vertical axis) and the temperature (horizontal axis) and look in which phase is it located:liquid, solid, gaseous or supercritical fluid (a phase only present at high temperatures and/or pressures above the critical point, has properties of liquids and gas).
To use our phase diagram, we convert our temperature from Celsius to Kelvin, adding 273.15 K (0°C=273.15 K), i.e. the temperature we are looking for in our diagram is 373.15 K.
Looking where is the point located, we determine that water at 100°C and 500 kPa is in the liquid phase.