What does the white powder in a Class B fire extinguisher do?

The white powder in a Class B fire extinguisher is typically a dry chemical agent, such as sodium bicarbonate, potassium bicarbonate, or magnesium chloride. The primary function of this powder is to interrupt the chemical reaction that fuels a fire. Fire is sustained by a chemical reaction involving heat, fuel, and an oxidizer; dry chemical agents can disrupt this reaction by forming a barrier between the combustibles and the oxidizer, effectively stopping the fire from continuing to burn.

In contrast, other choices suggest actions that do not accurately represent the primary mechanism of dry chemical agents. While it is true that some fire extinguishers can cool the fire or smother flames, these are not the specific functions of the white powder found in a Class B extinguisher. Instead, the focus here is on the powder's ability to chemically interrupt the fire's combustion process, making it a highly effective tool for dealing with flammable liquids and gases.