**Core Concept:** Reflux nephropathy is a condition caused by the backflow of urine from the bladder into the ureter, leading to tubular damage and inflammation. Nephrotic range proteinuria occurs when the glomerular filtration barrier is severely damaged, causing protein loss in the urine. Nephrotic range proteinuria is a clinical sign of glomerular disease.

**Why the Correct Answer is Right:** In reflux nephropathy, the damaged tubules in the kidneys result in protein loss due to the disrupted glomerular filtration barrier. This leads to nephrotic range proteinuria. The correct answer, **C. Interstitial fibrosis and tubular atrophy**, describes the histological changes that occur in response to tubular damage and inflammation.

**Why Each Wrong Option is Incorrect:**

A. **Interstitial nephritis:** Although inflammation may occur, this option does not specifically address the histological finding of nephrotic range proteinuria in reflux nephropathy.

B. **Glomerulonephritis:** Reflux nephropathy primarily affects the tubules, not the glomeruli. This option does not align with the clinical scenario.

D. **Interstitial nephritis:** Similar to option A, this option does not directly address the nephrotic range proteinuria associated with reflux nephropathy.

**Clinical Pearl:** In nephrotic range proteinuria, the presence of histological findings like **interstitial fibrosis and tubular atrophy** is crucial in confirming the diagnosis of reflux nephropathy. These changes indicate tubular damage and inflammation resulting in protein loss. Understanding these histopathological features is essential for accurate diagnosis and appropriate management in clinical practice.