What characterizes a flammable gas?

A flammable gas is defined by its ability to ignite and combust when mixed with air in specific concentrations. The characteristics of flammable gases emphasize that there is a certain range of concentration—known as the lower and upper explosive limits—within which the gas can sustain combustion when an ignition source is present.

This definition is critical in safety regulations and operational practices, especially in environments where medical gases are used. Understanding this property allows for the implementation of appropriate safety measures, such as ventilation, monitoring, and handling procedures to prevent accidental ignition.

The other options do not accurately represent the definition of a flammable gas. A liquid that evaporates at room temperature pertains to volatile liquids rather than gases, non-toxic and harmless gases do not indicate flammability, and the assertion that a gas can only burn in high-pressure conditions is misleading, as many flammable gases can ignite at normal atmospheric pressure under suitable conditions.