**Core Concept**
The sodium-potassium pump is an essential ATP-dependent transport mechanism responsible for maintaining the electrochemical gradients of sodium (Na+) and potassium (K+) ions across the cell membrane. This process is crucial for neuronal function, muscle contraction, and overall cellular homeostasis.

**Why the Correct Answer is Right**
The sodium-potassium pump, also known as Na+/K+-ATPase, utilizes the energy from ATP hydrolysis to transport three sodium ions out of the cell and two potassium ions into the cell against their concentration gradients. This pump is primarily located in the plasma membrane of cells and plays a vital role in regulating the balance of sodium and potassium ions, which is essential for maintaining the resting membrane potential and facilitating various cellular functions.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the sodium-potassium pump is not a receptor-mediated process. It is an enzyme-driven transport mechanism that does not involve receptor-ligand interactions.
**Option B:** Incorrect because the sodium-potassium pump does not involve the direct movement of water across the cell membrane. While it does affect the balance of ions, its primary function is not osmoregulation.
**Option C:** Incorrect because the sodium-potassium pump is not a passive transport mechanism. It requires the energy from ATP hydrolysis to function, making it an active transport process.

**Clinical Pearl / High-Yield Fact**
The sodium-potassium pump is inhibited by cardiac glycosides, such as digoxin, which are used to treat certain types of heart failure. This inhibition leads to an increase in intracellular sodium and a decrease in intracellular potassium, resulting in a decrease in the contractility of the heart muscle.

**Correct Answer:** C. Sodium-potassium pump