Final answer:
Chloride (Cl-) is the most abundant anion in the ECF. It is essential for maintaining hydration, balancing cations in the ECF, and creating osmotic pressure. Chloride ions follow the same paths as sodium ions in the renal system.
Step-by-step explanation:
Chloride (Cl-) is the most abundant anion in the Extracellular Fluid (ECF). It plays a vital role in maintaining proper hydration and balancing cations in the ECF. Chloride is also a major contributor to the osmotic pressure gradient between the Intracellular Fluid (ICF) and ECF. The paths of secretion and reabsorption of chloride ions in the renal system follow the paths of sodium ions.