ANS:B - blanketting the area with nitrogen atmosphere.

Fire in fuel gas pipelines is extinguished most effectively by blanketing the area with a nitrogen atmosphere. Explanation: When a fire occurs in fuel gas pipelines, it's essential to eliminate the oxygen supply to extinguish the fire effectively. Blanketing the area with a nitrogen atmosphere achieves this by displacing the oxygen and creating an inert environment, which prevents combustion. Spraying water may not be effective for extinguishing fires in fuel gas pipelines because it can cause spreading of the fire or even explosion due to the reactive nature of some fuel gases with water. Similarly, fire fighting foam may not be suitable for extinguishing fires in fuel gas pipelines as it may not effectively smother the fire or displace the oxygen. Therefore, blanketing the area with a nitrogen atmosphere is the most effective method for extinguishing fires in fuel gas pipelines.