Which ion predominantly serves as the main electrolyte in the extracellular fluid (ECF)?

Explanation

The primary electrolyte in the extracellular fluid is sodium (Na+), which plays a crucial role in maintaining fluid balance and nerve function. Potassium (K+) is mainly found inside cells, chloride (Cl-) is also present in ECF but not the main cation, and proteins are more abundant in intracellular fluid.