## Core Concept
The question tests the understanding of the nephrotoxic effects of mercury on the renal tubules. Mercury is a heavy metal known to cause renal damage. The renal tubules are composed of different segments, each with distinct functions and susceptibilities to toxins.

## Why the Correct Answer is Right
Mercury primarily affects the **proximal convoluted tubule (PCT)** of the renal tubule. The PCT is responsible for the reabsorption of glucose, amino acids, and ions back into the bloodstream. Mercury's toxic effect on the PCT leads to **acute tubular necrosis (ATN)**, a condition characterized by the death of tubular epithelial cells, which can lead to acute kidney injury. The mechanism involves the accumulation of mercury in the renal tubular cells, leading to cellular damage and necrosis.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because mercury's primary toxic effect is not on the **loop of Henle**, although heavy metals can affect multiple parts of the nephron.
* **Option B:** This option is incorrect as mercury does not specifically target the **distal convoluted tubule** as its primary site of action.
* **Option D:** This option is incorrect because the **collecting duct** is not the primary site of mercury toxicity.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **mercury and other heavy metals** can cause **acute kidney injury (AKI)** through **proximal tubular damage**. This is a critical concept in nephrology and toxicology, as identifying the cause of AKI can guide treatment.

## Correct Answer: C. Proximal convoluted tubule.