**Core Concept**
Distal renal tubular acidosis (dRTA) is a disorder of the distal nephron characterized by impaired hydrogen ion secretion and impaired ammonium ion production, leading to a failure to acidify the urine adequately in response to systemic acidosis. This results in metabolic acidosis, with or without hypokalemia, and often accompanied by hypercalciuria and nephrocalcinosis.

**Why the Correct Answer is Right**
The correct answer is associated with the pathophysiology of dRTA, specifically the inability to secrete hydrogen ions in the collecting duct. This is due to impaired function of the H+-ATPase pump in the alpha-intercalated cells of the collecting duct. As a result, the urine remains alkaline, even in the presence of systemic acidosis, and the body loses potassium ions in exchange for hydrogen ions. This leads to hypokalemia, which is a hallmark of dRTA.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not directly related to the pathophysiology of dRTA. While hyperphosphatemia can be seen in dRTA due to impaired phosphate excretion, it is not a defining feature of the condition.
* **Option B:** This is not a characteristic of dRTA. In fact, hypokalemia is a common finding in dRTA, not hyperkalemia. Hyperkalemia is more commonly seen in proximal RTA.
* **Option C:** This is not a defining feature of dRTA. While nephrocalcinosis can occur in dRTA due to hypercalciuria, it is not a specific association.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of dRTA is the presence of "renal tubular acidosis" in the urine, despite systemic acidosis, which can be detected using a urine pH test. This is a critical diagnostic clue that distinguishes dRTA from other causes of metabolic acidosis.

**Correct Answer: C. Nephrocalcinosis.**