What is the most common substance that is dissolved in ocean water?
The most common substance dissolved in ocean water is sodium chloride.
Ocean water contains a number of substances. When a substance which has ionic bonds is dissolved in water it takes the form of ions.
The most common ions in ocean water are sodium and chloride. These are the ions formed when common salt, sodium chloride (NaCl) is dissolved in water.
Sodium chloride accounts for about 3% of ocean water by mass.