Which of the following is the principal constituent in water that causes corrosion of metals?

Dissolved oxygen is the principal constituent in water that causes the corrosion of metals. When oxygen dissolves in water, it can react with metal surfaces, leading to oxidation, which is a fundamental process in corrosion. This reaction forms metal oxides, which can weaken the structure of metal objects over time. In environments where oxygen is present, particularly in flowing or stagnant water, corrosion rates can increase significantly.

The presence of dissolved oxygen is critical, as it is a strong oxidizing agent that can facilitate electrochemical reactions, which are central to the corrosion process. This makes controlling the levels of dissolved oxygen essential in water treatment and metal preservation strategies to minimize corrosion-related damage.