Which of the following is the most abundant extracellular ion?
Calcium
Potassium
Sodium
Chloride
Sodium is the most abundant extracellular ion, whereas potassium is the most abundant intracellular ion. Phosphate is the most abundant intracellular anion and chloride is the most abundant extracellular anion. Ref: Human anatomy and physiology By Elaine N. Marieb, Katja Hoehn, 2010, Page 625; Guyton's physiology 11th edition page 46, 358.