**Core Concept**
The Na+ - K+ pump, also known as the sodium-potassium pump, is an enzyme that maintains the electrochemical gradient of sodium and potassium ions across the cell membrane. It is a critical component of the cell's resting membrane potential and plays a key role in various cellular processes, including nerve conduction and muscle contraction.

**Why the Correct Answer is Right**
The Na+ - K+ pump uses the energy from ATP hydrolysis to pump three sodium ions out of the cell and two potassium ions into the cell against their concentration gradients. This process is essential for maintaining the cell's resting membrane potential, which is approximately -70 millivolts due to the selective permeability of the cell membrane to potassium ions. The Na+ - K+ pump is an example of a secondary active transport mechanism, where the energy from ATP hydrolysis is used to transport ions against their concentration gradients.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the function of the Na+ - K+ pump. While it is true that the Na+ - K+ pump uses energy from ATP hydrolysis, it does not pump equal numbers of sodium and potassium ions.
**Option B:** This option is incorrect because it is not a characteristic of the Na+ - K+ pump. The Na+ - K+ pump is not an example of a primary active transport mechanism, which would involve the direct use of ATP to transport ions against their concentration gradients.
**Option C:** This option is incorrect because it is not a specific enough description of the Na+ - K+ pump. While it is true that the Na+ - K+ pump uses energy from ATP hydrolysis, it is not accurate to say that it pumps all ions against their concentration gradients.

**Clinical Pearl / High-Yield Fact**
The Na+ - K+ pump is an essential component of the cell's resting membrane potential, and its dysfunction can lead to various clinical conditions, including hypertension, cardiac arrhythmias, and muscle weakness. In addition, the Na+ - K+ pump is sensitive to certain toxins, such as ouabain, which can inhibit its activity and lead to cardiac arrest.

**Correct Answer:** Not provided, please provide the correct options for the question.