Which of the following electrolyte is the chief extracellular cation?

Sodium (Na+) is recognized as the chief extracellular cation because it plays a vital role in maintaining fluid balance, osmotic pressure, and the proper functioning of cells throughout the body. Being the primary cation in the extracellular fluid, sodium is crucial for various physiological processes, including the generation and conduction of action potentials in nerve and muscle tissues.

Sodium's high concentration outside cells compared to potassium, which is primarily found inside cells, creates an electrochemical gradient necessary for cellular functions. This gradient affects processes such as nerve impulse transmission and muscle contraction, where rapid changes in sodium concentration across the cell membrane are essential.

In contrast, while potassium and calcium also have essential roles in cellular functions, they are not predominant in the extracellular space. Potassium, for instance, is mainly an intracellular cation, and calcium, though crucial for muscle contraction and neurotransmitter release, exists in much lower concentrations outside cells compared to sodium. Chloride functions mainly as an anion and is involved in maintaining electrical neutrality but doesn't serve the same cationic functions that sodium does. Thus, sodium’s role and concentration establish it as the primary extracellular cation.