What does a Class K fire extinguisher extinguish?

A Class K fire extinguisher is specifically designed to extinguish fires caused by cooking oils and fats, particularly those that are used in commercial kitchens, such as vegetable oils and animal fats. These fires can produce extremely high temperatures and are commonly found in fryers and cooking appliances. The Class K extinguisher uses a specialized extinguishing agent, often a wet chemical, that cools the flames and forms a barrier between the oxygen and the fuel, effectively suppressing the fire.

This makes option B the correct choice, as it directly addresses the type of fires the Class K extinguisher was developed to combat. Other classes, such as those for flammable gases, solid materials like wood and paper, or electrical devices, would be served by different types of extinguishers designed for specific fire hazards. Thus, recognizing the specific application of a Class K extinguisher is vital for effective fire safety practices in environments where cooking is prevalent.