When discharging a portable CO2 fire extinguisher, you should NOT hold the horn of the extinguisher because the horn __________.

Correct Answer: Option D — becomes extremely cold

Rapid expansion of liquid CO2 through the discharge horn drops temperatures to approximately -110°F (-79°C). Holding the bare horn directly can cause severe cryogenic frostbite or tissue freezing to human skin; operators must hold only the insulated handle.