Final answer:
Carbon dioxide fire extinguishers store CO₂ as a liquid under pressure, displace air, and the rapid expansion creates a cooling effect to extinguish fires. However, CO₂ is not decomposed by the extinguisher. The extinguisher's function depends on the critical temperature, which is 31 °C for CO₂, determining its state in different temperature conditions.
Step-by-step explanation:
The characteristics that describe a modern type of fire extinguisher include that it stores carbon dioxide under pressure as a liquid (A), and upon release, carbon dioxide displaces a large volume of air in the fire zone to smother the fire (B). In addition, the rapid expansion of CO₂ produces a cooling effect which helps to extinguish the fire (C). However, the characteristic that does not describe a modern fire extinguisher is (D) that it decomposes carbon dioxide to extinguish the fire. Fire extinguishers do not decompose CO₂; they utilize it as a suppression agent either in some combination of its ability to displace oxygen, cool the temperature, or both.
Understanding the behavior of CO₂ under pressure can be explained by looking at its critical temperature. The critical temperature of CO₂ is 304 K or 31 °C. Below this temperature, CO₂ can exist as a liquid under pressure within the extinguisher. If the temperature of the CO₂ exceeds the critical temperature, no amount of pressure can keep it in a liquid state, which is why we wouldn't find liquid CO₂ in a fire extinguisher on a hot day when the temperature is above 31 °C.