The correct option is Sodium chloride.
Explanation
Seawater is a complex solution containing various dissolved salts. The salinity of the ocean is defined by the total amount of dissolved solids in water. While many salts are present, a few specific compounds dominate the composition.
Analysis of Options
- Sodium Chloride (NaCl): This is the most abundant soluble salt in seawater, constituting approximately 77.8% of the total dissolved salts. It is the primary reason for the salty taste of ocean water.
- Magnesium Chloride (MgCl2): This is the second most abundant salt, accounting for roughly 10.9% of the total salt content.
- Calcium Carbonate (CaCO3): While present, it constitutes a very small fraction of dissolved salts compared to chlorides and sulphates. It is often utilized by marine organisms for shell formation.
- Copper Sulphide: This is not a major component of seawater salinity and is generally insoluble.
Key Takeaway
Sodium chloride is the predominant salt in seawater, followed by magnesium chloride, magnesium sulphate, and calcium sulphate.