**Core Concept**
The kidneys play a crucial role in maintaining acid-base balance by regulating bicarbonate reabsorption. The process involves the reabsorption of filtered bicarbonate ions in the renal tubules, which is essential for maintaining the body's pH homeostasis.

**Why the Correct Answer is Right**
The main site of bicarbonate reabsorption is the proximal convoluted tubule (PCT). The PCT has a high capacity for bicarbonate reabsorption, which accounts for approximately 70-80% of the filtered bicarbonate load. This process occurs through the action of carbonic anhydrase, an enzyme that catalyzes the reversible reaction between carbon dioxide and water to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions. The bicarbonate ions are then reabsorbed into the bloodstream via the sodium-bicarbonate cotransporter (NBCe1), while the hydrogen ions are either reabsorbed or secreted into the lumen.

**Why Each Wrong Option is Incorrect**
**Option A:** The distal convoluted tubule (DCT) also plays a role in bicarbonate reabsorption, but it is not the main site. The DCT reabsorbs bicarbonate through the action of type 2 Na+/H+ exchangers.
**Option B:** The collecting ducts are primarily involved in potassium and sodium reabsorption, not bicarbonate reabsorption.
**Option C:** The loop of Henle is primarily involved in water and ion reabsorption, but it does not play a significant role in bicarbonate reabsorption.

**Clinical Pearl / High-Yield Fact**
The kidneys have a limited capacity for bicarbonate reabsorption, and impaired renal function can lead to metabolic acidosis. In patients with chronic kidney disease, bicarbonate reabsorption is decreased, leading to a compensatory increase in respiratory rate to blow off carbon dioxide.

**Correct Answer: C. Proximal convoluted tubule (PCT).**