In extracellular fluid the most abundant cation is:.

Sodium

Explanation:

Extracellular fluid are the fluid that are found outside the cells of the body. The major components is interstitial and blood plasma. The most abundant cation in the extracellular fluid is sodium and this is because sodium responsible for about half of the osmotic pressure gradients which occur between the internal of the cells and their neighbouring environment and it also play a major role in maintaining homeostasis.

answer; /// i believe the correct answer is (reactants);