ANS:B - is corrosive.

Free oxygen is removed from boiler feed water primarily because it is corrosive. When water containing dissolved oxygen enters a boiler system, it can cause corrosion of the boiler's metal surfaces, piping, and other components. This corrosion can weaken the materials, leading to leaks, failures, and reduced equipment lifespan. The presence of oxygen can initiate various forms of corrosion, including oxygen pitting corrosion and oxygen-induced corrosion fatigue. These corrosion processes can significantly reduce the efficiency and safety of boiler systems, making it crucial to remove free oxygen from the feed water. While the presence of oxygen can indirectly affect heat transfer coefficients by promoting corrosion and fouling, its primary concern in boiler feed water treatment is its corrosive nature rather than its direct impact on heat transfer coefficients or causing explosions. Therefore, the correct answer is:

• It is corrosive.