Final answer:
Potassium bicarbonate is used as a dry chemical extinguishing agent; it is not ammonium nitrate, which can be unstable and is not used for this purpose.
Step-by-step explanation:
One chemical used as a dry chemical extinguishing agent is D. Potassium bicarbonate. It is effective in putting out class B (flammable liquids) and class C (electrical) fires. This chemical, when released from a fire extinguisher, creates a barrier between the fuel and the oxygen, extinguishing the fire. It's crucial to note that while ammonium nitrate is used in various industrial applications and can also be used in improvised explosives, it's not used as a fire extinguishing agent due to its potential for instability and explosion under certain conditions, as evidenced in historical incidents such as the Texas City disaster.