**Question:** Ratio of concentration of the sodium ions inside the cells to that of outside the cells:

A. 3:1
B. 2:1
C. 1:1
D. 4:1

**Core Concept:** **Sodium-Potassium Pump and Electrolyte Homeostasis:**

The correct answer is **B. 2:1**. The ratio of the concentration of sodium ions inside the cells to that of outside the cells is 2:1 in most cells of the human body. This is due to the crucial role of the sodium-potassium pump, an active transporter found in the cell membrane that maintains the electrochemical gradient by actively transporting three sodium ions out of the cell for every two potassium ions moving into the cell.

The sodium-potassium pump (Na+/K+-ATPase) is essential for maintaining electrochemical balance and cellular homeostasis. It is a primary determinant of the resting membrane potential and plays a vital role in nerve and muscle function.

**Why the Correct Answer is Right:**

The sodium-potassium pump is a crucial element in maintaining the electrochemical gradient and cellular homeostasis. By actively transporting three sodium ions out of the cell for every two potassium ions moving into the cell, it helps to keep the sodium concentration inside the cell lower than that outside the cell, which is why the ratio is 2:1.

**Why Each Wrong Option is Incorrect:**

A. 3:1 is incorrect because it does not represent the exact ratio of sodium ions to potassium ions maintained by the sodium-potassium pump.
C. 1:1 is incorrect as it does not reflect the actual ratio maintained by the sodium-potassium pump.
D. 4:1 is incorrect because it deviates from the correct ratio of 2:1.

**Clinical Pearl:**

Understanding the role of the sodium-potassium pump in maintaining cellular homeostasis is essential for understanding cellular function, nerve impulse transmission, muscle contraction, and the maintenance of resting membrane potential. A proper understanding of this concept is crucial for students studying physiology, pharmacology, and clinical medicine.