Final answer:
Sodium Chloride (NaCl) is the greatest dissolved solid in ocean water, containing the most abundant ions contributing to salinity compared to other substances like Magnesium.
Step-by-step explanation:
The greatest dissolved solid in ocean water is Sodium Chloride (NaCl). Ocean water consists primarily of various salts, and Sodium Chloride is the most abundant.
While seawater contains many different ions and compounds, the ions from Sodium Chloride, sodium (Na+) and chloride (Cl-), make up the majority of the salinity.
Magnesium in the form of Mg2+ is also present in ocean water, but in smaller quantities compared to Sodium Chloride.