**Core Concept**
Na+-1C+ ATPase, also known as the sodium-potassium pump, is a transmembrane enzyme responsible for maintaining the electrochemical gradient across cell membranes by pumping sodium ions out of the cell and potassium ions into the cell against their concentration gradients, utilizing energy from ATP hydrolysis.

**Why the Correct Answer is Right**
The sodium-potassium pump is essential for maintaining the resting membrane potential and regulating the intracellular concentration of sodium and potassium ions. It works by binding to ATP and hydrolyzing it to ADP and Pi, which drives the transport of three sodium ions out of the cell and two potassium ions into the cell. This process requires the presence of a specific enzyme, Na+-K+-ATPase, which is a transmembrane protein embedded in the plasma membrane.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Na+-1C+ ATPase is not a calcium pump; it is a sodium-potassium pump.
**Option B:** This option is incorrect because Na+-1C+ ATPase is not a sodium-calcium exchanger; it is a primary active transport mechanism that uses ATP hydrolysis to pump ions against their concentration gradients.
**Option C:** This option is incorrect because Na+-1C+ ATPase is not a part of the Na+/H+ exchanger; it is a separate enzyme responsible for maintaining the sodium-potassium gradient.

**Clinical Pearl / High-Yield Fact**
The sodium-potassium pump is essential for maintaining proper cellular function, and its dysfunction can lead to various diseases, including hypertension, cardiac arrhythmias, and neurological disorders. Digitalis, a cardiac glycoside, works by inhibiting the sodium-potassium pump, leading to an increase in intracellular sodium and a subsequent increase in intracellular calcium, which enhances cardiac contractility.

**Correct Answer:** D.