Correct Answer:
A. Chlorine
Chlorine is the element present in abundance in seawater, primarily in the form of chloride ions (Cl-), which combine with sodium ions to form sodium chloride (common salt). Seawater is a complex solution, but chloride is the most abundant anion, contributing significantly to its salinity.
- Oxygen (B) is present, but mostly dissolved as O2 gas, not as abundant as chloride ions.
- Calcium (C) is an important ion in seawater, but less abundant than chloride or sodium.
- Iron (D) is a trace element in seawater, present in very small concentrations compared to major ions like chloride.