**Core Concept**
The kidneys play a crucial role in maintaining electrolyte and fluid balance by regulating the reabsorption and excretion of various substances through the renal tubules. The reabsorption of substances such as glucose, amino acids, and ions occurs primarily in the proximal convoluted tubule (PCT), while other substances like urea and uric acid are reabsorbed to a lesser extent.

**Why the Correct Answer is Right**
Urea is minimally reabsorbed through the renal tubules due to the presence of urea transporters (UT-A and UT-B) in the collecting ducts. However, the primary mechanism of urea reabsorption is through the countercurrent multiplier system in the medulla, which creates a high concentration of urea in the interstitium. This allows for passive reabsorption of urea back into the bloodstream. The minimal reabsorption of urea is essential for maintaining the osmotic gradient in the medulla, which is necessary for water reabsorption and concentration of the urine.

**Why Each Wrong Option is Incorrect**
**Option A:** Glucose is almost completely reabsorbed through the renal tubules via the sodium-glucose cotransporter 2 (SGLT2) in the PCT. This occurs before glucose reaches the distal parts of the tubules.
**Option B:** Bicarbonate (HCO3-) is reabsorbed in the PCT and the distal convoluted tubule (DCT) through the bicarbonate reabsorption mechanism, which involves the enzyme carbonic anhydrase.
**Option D:** Uric acid is reabsorbed in the PCT and the DCT through the urate transporters (URAT1 and OAT1), but its reabsorption is not as minimal as urea's.

**Clinical Pearl / High-Yield Fact**
The kidneys' ability to concentrate or dilute the urine is essential for maintaining fluid balance and blood pressure. The minimal reabsorption of urea in the renal tubules allows for the proper functioning of the countercurrent multiplier system, which is critical for urine concentration.

**✓ Correct Answer: C. Urea**