Which of the following is NOT a type of fire extinguisher?

The correct answer is the mechanical extinguisher, as it does not represent a recognized type of fire extinguisher. Fire extinguishers are categorized based on the agents they use to suppress fires and the classes of fires they are designed to combat.

Foam extinguishers are specifically designed to extinguish fires involving flammable liquids and are effective due to their ability to form a barrier between the fuel and the fire. Water extinguishers are also a common type, used primarily for Class A fires involving ordinary combustibles such as wood, paper, and textiles. CO2 (carbon dioxide) extinguishers are effective for Class B fires involving flammable liquids and electrical fires, as the CO2 displaces oxygen and suffocates the fire.

In contrast, a mechanical extinguisher is not a standard classification or type within fire safety protocols. Fire extinguishers operate on various principles—involving chemical reactions or physical means of cooling, smothering, or displacing oxygen—but the term "mechanical extender" does not correspond to any known or standard fire extinguishing technology.