**Core Concept**
Nephrocalcinosis is a condition characterized by the deposition of calcium salts in the renal tissue, leading to renal damage and dysfunction. This condition can be caused by various factors, including metabolic disorders, kidney stone formation, and certain medications.

**Why the Correct Answer is Right**
Nephrocalcinosis can be caused by hyperparathyroidism, which leads to an excess of parathyroid hormone (PTH) in the body. Elevated PTH levels stimulate the kidneys to reabsorb more calcium from the urine, resulting in increased calcium levels in the blood and its subsequent deposition in the renal tissue. Another cause is idiopathic hypercalciuria, a condition characterized by excessive urinary excretion of calcium, which can lead to the formation of calcium stones and subsequent nephrocalcinosis. Additionally, certain medications such as furosemide can cause nephrocalcinosis by increasing calcium excretion in the urine.

**Why Each Wrong Option is Incorrect**
**Option A:** Hyperkalemia is not a direct cause of nephrocalcinosis, although it can be a complication of kidney disease that may lead to nephrocalcinosis.
**Option B:** Hypokalemia is not a direct cause of nephrocalcinosis, although it can be a consequence of certain conditions that lead to nephrocalcinosis.
**Option C:** Hyperphosphatemia is not a direct cause of nephrocalcinosis, although it can be a complication of kidney disease that may lead to nephrocalcinosis.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that nephrocalcinosis can be asymptomatic in its early stages, and diagnosis often relies on imaging studies such as X-rays or CT scans. Regular monitoring of calcium and PTH levels is essential in patients with conditions that increase the risk of nephrocalcinosis.

**Correct Answer: D.**