Final answer:
Ocean acidification occurs when carbon dioxide dissolves in ocean water and forms carbonic acid, which lowers ocean pH.
Step-by-step explanation:
Ocean acidification is the process of ocean waters decreasing in pH. The most likely chemical reaction that contributes to the change in ocean pH is when carbon dioxide (CO2) interacts with ocean water to form carbonic acid, which lowers ocean pH. This is because carbon dioxide dissolves in the ocean and reacts with water to produce carbonic acid, which releases hydrogen ions (H+) and lowers the pH of the water. As more CO2 is released into the atmosphere, more of it dissolves in the ocean and contributes to ocean acidification.