What typically characterizes compressed gases?

The characterization of compressed gases is best described by the statement that they may be liquefied or non-liquefied at a standard temperature, such as 68°F. Compressed gases can exist in various states depending on conditions such as temperature and pressure. At certain temperatures and pressures, gases can change to a liquid state. The ability to be liquefied or to remain in a gaseous state under varying conditions is a fundamental property of gases, particularly those stored in pressurized containers.

The other options do not adequately define compressed gases. For example, the notion of gases being only in a liquid state under normal pressure is inaccurate, as many gases will remain gaseous unless specific conditions are met. Mixtures of solid and liquid materials are distinct from the definition of gases, which strictly pertain to the state of matter at given conditions, and limitations concerning toxicity and hazards do not encompass the broader characteristics of gases, which can include both harmful and benign substances.