A fire extinguisher containing compressed CO2 is used to put out a fire. In spite of being close to the flames, the firefighter notices a white layer of "frost" forming on the exterior of the fire extinguisher can. What's going on?
A) The gas in the extinguisher is expanding when released, cooling adiabatically.
B) The gas in the extinguisher is cooling under higher pressure.
C) The exterior temperature must be dropping.
D) The fire is pulling heat from the surrounding air.

A) The gas in the extinguisher is expanding when released, cooling adiabatically.

Explanation:

Adiabatic cooling occurs when a previously high temperature gas such as CO2 cools on release due to an increase in volume. In the fire extinguisher tank the temperature of CO2 is high due to the reduced volume and higher pressure, but when it is released to the environment, the volume increases which leads to cooling.  Adiabatic cooling is the process of reducing heat through a change in air pressure caused by volume expansion.