Which characteristic refers to high-pressure gas?

The characteristic that refers to high-pressure gas is indicated by the full pressure range of 1,800-2,000 psi. In the context of gaseous states, "high-pressure" typically describes those gases that are stored or utilized at elevated pressure levels, significantly above atmospheric pressure.

This pressure range is commonly associated with compressed gases used in various aviation and industrial applications, such as oxygen or nitrogen. High-pressure storage allows for a greater volume of gas to be contained in a smaller space, which is crucial for efficient use in aircraft systems, particularly for maintaining crew safety and sustaining cabin environments.

The other options represent different attributes associated with gas cylinders but do not define high-pressure gas accurately. For instance, while a full pressure of 400-450 psi may be relevant to specific applications, it is not categorized within the typical high-pressure range. Green cylinders may identify specific gas types, such as oxygen, but do not inherently represent pressure characteristics. Lastly, an empty pressure of 100 psi indicates a low residual amount of gas, which does not align with the concept of high pressure at all.