Final answer:
CO2 fire extinguishers contain liquid CO2 when internal temperatures are below the critical temperature of 31°C; above this, CO2 can't be liquefied. They extinguish fires by displacing oxygen, but they can't be used on magnesium fires.
Step-by-step explanation:
The characteristics of CO2 fire extinguishers are influenced by the properties of carbon dioxide, particularly its critical temperature. On a cool day with temperatures below 31°C (304 K), the internal temperature of a CO2 fire extinguisher is less than the critical temperature of CO2, which allows liquid CO2 to exist inside the cylinder. This is why we can hear liquid sloshing around. However, on a hot day when temperatures exceed the critical temperature of CO2, the gas cannot be liquefied irrespective of the pressure applied; thus, no liquid CO2 sloshing is observed inside the extinguisher.
It is worth noting that CO2 fire extinguishers are effective in putting out fires by displacing oxygen, as CO2 is heavier than air. However, CO2 extinguishers are not suitable for all types of fires; for instance, they cannot extinguish magnesium fires as the reaction between CO2 and magnesium produces magnesium oxide and carbon, rather than putting out the fire.