Final answer:
A sample of pure X, if it is a gas, would be at a higher temperature and lower pressure, though the specific region cannot be determined without a phase diagram.
Step-by-step explanation:
If a sample of pure X is a gas, the temperature and pressure must be in a region where substances typically exist in the gaseous state. Based on the phase diagram descriptions provided, a gas exists at conditions of low pressure and high temperature. A phase diagram typically shows different regions where a substance exists as a solid, liquid, or gas based on different pressures and temperatures. Therefore, the sample of pure X must be in a region on the phase diagram indicative of gaseous conditions, which is not specified in the provided options (a. Region f, b. Region g, c. Region h, d. Region d) since the question does not include a phase diagram. However, other contextual clues from the given information, such as the behavior of real gases and the examples of gas conditions at specific temperatures and pressures, suggest that gases tend to exist at higher temperatures and lower pressures.