Which of the following states the correct principle of fire extinguishers?

Answer: B

Solution:

The principle of a fire extinguisher is to cut off the air supply and cool the burning substance below its ignition temperature. 

There are three essential requirements for producing fire. These are fuel, air (to supply oxygen), and heat (to raise the temperature of the fuel beyond the ignition temperature). Fire can be controlled by removing one or more of these requirements. The job of a fire extinguisher is to cut off the supply of air or bring down the temperature of the fuel, or both. So option B is the correct option