Question

The most abundant mineral of extracellular fluid is
(a). Calcium
(b). Potassium
(c). Sodium
(d). Phosphate

Answer 1

Hint: It is the major cation in the extracellular fluid (ECF) and as such is the major contributor to the ECF osmotic pressure and ECF compartment volume. The loss of water from the ECF compartment increases its concentration, and this condition is called hypernatremia. Isotonic loss of water and this mineral from the ECF compartment decreases the size of that compartment in a condition called ECF hypovolemia.

Complete answer
Sodium is the most abundant mineral found within the extracellular fluids. It plays an important role in maintaining water balance in blood and tissues. Excess sodium in the body causes hypernatremia with the loss of a large amount of water in the body. While insufficient sodium also can be dangerous for the body.

Additional information
The ECF provides the medium for the exchange of drugs between the ECF and therefore the cells, and this will happen through dissolving, mixing, and transporting within the fluid medium. Substances within the ECF include dissolved gases, nutrients, and electrolytes, all needed to take care of life. The ECF also contains materials secreted from cells in soluble form, but which quickly coalesces into fibers (e.g. collagen, reticular, and elastic fibers) or precipitates out into a solid or semisolid form (e.g. proteoglycans which form the bulk of cartilage, and the components of bone). These and heaps of different substances happen, particularly in relationships with different proteoglycans to make the extracellular framework or the "filler" substance between the cells all through the body. These substances occur within the extracellular space and are therefore all bathed or soaked in ECF, without being a part of the ECF.

So the correct answer is ‘Sodium’.

Note: The extracellular fluid, in particular the interstitial fluid, constitutes the body's internal environment that bathes all of the cells in the body. The ECF composition is therefore crucial for his or her normal functions and is maintained by a variety of homeostatic mechanisms involving feedback. Homeostasis regulates, among others, the pH, sodium, potassium, and calcium concentrations within the ECF. The volume of liquid body substance, blood sugar, oxygen, and carbon dioxide levels also are tightly homeostatically maintained.