Which term describes a substance that at 50°C has a vapor pressure greater than 300 kPa or is completely gaseous at 20°C?

• A. Compressed Gas
• B. Gas
• C. Liquefied Gas
• D. Dissolved Gas

Answer: (B)

Gas is defined by air transport rules as a substance that either at 50°C has a vapor pressure of 300 kPa or more, or is completely gaseous at 20°C. This means the substance behaves as a gas under typical transport conditions either because it already is a gas at room temperature or because its vapor pressure is high enough to push it into the gaseous category at elevated temperature. The 300 kPa (3 bar) threshold is the cutoff used to distinguish gases from liquefied or dissolved forms. Liquefied gases are those that can be liquefied under pressure and typically do not stay purely gaseous at room temperature, while dissolved gases are gases combined with a solvent. Packaging terms like compressed gas describe how the substance is stored, not its intrinsic classification by vapor pressure. Hence the correct term is Gas.