Final answer:
Intracellular fluid (ICF) is the fluid within cells and has a low concentration of sodium, while the extracellular fluid (ECF) like blood plasma has a high concentration of sodium.
Step-by-step explanation:
Intracellular fluid (ICF) is the fluid that resides within cells and is the principal component of the cytosol or cytoplasm. ICF makes up about 60 percent of the body's total water content. The chief cations in intracellular fluid are potassium (K+) and magnesium (Mg2+), with a lower amount of sodium (Na+).
The extracellular fluid (ECF), on the other hand, encompasses all fluids outside of cells, including blood plasma and interstitial fluid, with sodium being the principal ion. While the intracellular fluid has a low concentration of Na+, the extracellular fluid, including blood plasma, has a considerably higher concentration of sodium. Normal sodium concentrations are about ten times higher outside the cells than inside.