**Core Concept**
The **nephron** is the functional unit of the kidney, responsible for filtering waste and excess substances from the blood. **Potassium reabsorption** is a critical process that helps maintain electrolyte balance. The **proximal convoluted tubule (PCT)**, **loop of Henle**, **distal convoluted tubule (DCT)**, and **collecting duct** are key sites for potassium handling.

**Why the Correct Answer is Right**
Maximum potassium reabsorption occurs in the **proximal convoluted tubule (PCT)**. Here, approximately 65-70% of filtered potassium is reabsorbed, largely following the reabsorption of **sodium** and **water**. This process is mediated by the **sodium-potassium pump** and **potassium channels**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while some potassium reabsorption does occur here, it's not the primary site.
**Option B:** Incorrect as the loop of Henle has a role in potassium reabsorption but not to the extent of the PCT.
**Option D:** Incorrect because the collecting duct is more involved in potassium secretion.

**Clinical Pearl / High-Yield Fact**
Remember, the majority of potassium reabsorption happens early in the nephron, specifically in the PCT, which is crucial for maintaining potassium balance.

**Correct Answer:** B. Proximal convoluted tubule.