**Core Concept**
Potassium absorption in the jejunum is a crucial process for maintaining electrolyte balance in the body. The jejunum, a part of the small intestine, plays a significant role in the absorption of various nutrients, including electrolytes like potassium. This process is primarily facilitated by specific transport mechanisms that allow potassium ions to cross the intestinal epithelial cells.

**Why the Correct Answer is Right**
Potassium is absorbed in the jejunum through the process of co-transport with sodium and chloride ions. This is mediated by the Na+/K+-2Cl- cotransporter (NKCC1), which is present in the apical membrane of the enterocytes. As sodium and chloride ions enter the enterocyte, potassium ions follow, resulting in the absorption of potassium ions into the bloodstream. This process is essential for maintaining the proper balance of potassium ions in the body, which is critical for various cellular functions, including muscle contraction and nerve conduction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because potassium absorption in the jejunum is not primarily facilitated by the Na+/Ca2+ exchanger, which is involved in calcium transport.
**Option B:** This option is incorrect because the Na+/K+-ATPase pump is actually responsible for pumping potassium ions out of the cell, rather than absorbing them.
**Option C:** This option is incorrect because the H+/K+-ATPase pump is primarily involved in gastric acid secretion, rather than potassium absorption.

**Clinical Pearl / High-Yield Fact**
The jejunum plays a crucial role in potassium absorption, and impaired potassium absorption in this region can lead to hypokalemia, a condition characterized by low potassium levels in the blood. This can result in muscle weakness, fatigue, and cardiac arrhythmias.

**Correct Answer: D.**