Which statement correctly describes the relative abundance of electrolytes in the extracellular fluid (ECF) and intracellular fluid (ICF)?

• A. Potassium ions (K^+) are more abundant in the ECF, while sodium ions (Na^+) are more abundant in the ICF.
• B. Both sodium ions (Na^+) and potassium ions (K^+) are equally abundant in the ECF and ICF.
• C. Sodium ions (Na^+) are more abundant in the ECF, while potassium ions (K^+) are more abundant in the ICF.
• D. Chloride ions (Cl^-) are more abundant in the ICF than in the ECF.

Answer: (C)

Verified step by step guidance

1. Understand the context: The problem is about the relative abundance of electrolytes in two main fluid compartments of the body — extracellular fluid (ECF) and intracellular fluid (ICF). Electrolytes are ions that carry electrical charges and are essential for many physiological functions.
2. Recall the typical distribution of key electrolytes: Sodium ions (Na^+) and chloride ions (Cl^-) are generally more concentrated in the extracellular fluid (ECF), while potassium ions (K^+) are more concentrated inside cells, in the intracellular fluid (ICF).
3. Analyze each statement based on this knowledge: For example, the statement 'Potassium ions (K^+) are more abundant in the ECF' contradicts the known distribution because K^+ is primarily inside cells (ICF). Similarly, 'Both sodium ions (Na^+) and potassium ions (K^+) are equally abundant in the ECF and ICF' is incorrect because their concentrations differ significantly between compartments.
4. Confirm the correct statement: 'Sodium ions (Na^+) are more abundant in the ECF, while potassium ions (K^+) are more abundant in the ICF' aligns with physiological facts. Also, chloride ions (Cl^-) are more abundant in the ECF, not the ICF, so the last statement is incorrect.
5. Summarize the key concept: The selective distribution of electrolytes across cell membranes is maintained by active transport mechanisms (like the sodium-potassium pump), which keep Na^+ high outside cells and K^+ high inside cells, crucial for cell function and electrical activity.