Final answer:
The electron transport complex that participates in the reaction where oxygen is reduced to water, contributing to metabolic water production, is Complex IV, also known as cytochrome c oxidase.
Step-by-step explanation:
The reaction you've described involves the reduction of oxygen to form water, which happens in the electron transport chain, specifically at Complex IV, also known as cytochrome c oxidase. This complex contains cytochrome proteins c, a, and a3, with two heme groups and three copper ions. Complex IV is responsible for using the energy from electrons to pump hydrogen ions to the intermembrane space and facilitates the reduction of oxygen to water, finalizing the electron transport chain's role in oxidative phosphorylation.