Final answer:
A low concentration of both K+ ions and proteins would be found in the extracellular fluid, more specifically in plasma, interstitial fluid, and extracellular fluid more broadly, due to the function of the sodium-potassium pumps maintaining high concentrations of sodium in the extracellular space. The correct answer is B).
Step-by-step explanation:
You would find a low concentration of both K+ ions and proteins in the extracellular fluid (B) plasma, (C) interstitial fluid, and broadly speaking (D) extracellular fluid. The intracellular fluid (A) contains high amounts of potassium (K+) and proteins, which is consistent with its role in cellular functions.
Intracellular fluid is where chief cations like potassium (K+) and molecules such as proteins are abundant, so this compartment isn't where you'd find low concentrations of either. The extracellular fluid, which includes plasma and interstitial fluid, has higher concentrations of sodium (Na+) and chloride (Cl-), with low concentrations of K+ and proteins. The sodium-potassium pumps in cell membranes work to maintain these concentration gradients by actively pumping K+ into cells while removing Na+ from them.
For the student's related question, the sodium ion (Na+) is at the highest concentration in the (B) extracellular fluid.