The correct answer is B. CO2.
Oxygen (O2) is a fire accelerant, not an extinguishant. It is necessary for combustion to occur, so adding more oxygen will make a fire burn hotter and faster.
Carbon dioxide (CO2) is a fire extinguishant. It works by smothering the fire, depriving it of oxygen. It is also non-toxic and non-conductive, making it a safe and effective fire extinguishant for a variety of applications.
Sulfur dioxide (SO2) is a fire extinguishant, but it is not as effective as CO2. It works by breaking down the chemical bonds in the fuel, making it difficult for the fire to continue burning. However, SO2 is also toxic and corrosive, so it is not used as a fire extinguishant in many applications.
Nitrogen dioxide (NO2) is not a fire extinguishant. It is a gas that is produced when fuels are burned incompletely. NO2 is toxic and corrosive, and it can contribute to the formation of acid rain.
In conclusion, the correct answer is B. CO2.