**Core Concept**
The question is testing the student's understanding of the pathophysiology of nephrotic syndrome, particularly the ultrastructural changes that occur in the glomeruli of affected patients. The underlying principle involves the altered permeability of the glomerular filtration barrier, leading to massive proteinuria.

**Why the Correct Answer is Right**
The patient's presentation of generalized edema, marked albuminuria, hypoalbuminemia, and hyperlipidemia is classic for nephrotic syndrome. Electron microscopy is the gold standard for diagnosing certain types of nephrotic syndrome, such as minimal change disease (MCD). In MCD, the glomerular epithelial cells, also known as podocytes, exhibit effacement or fusion of their foot processes, leading to disruption of the glomerular filtration barrier. This results in the loss of large amounts of albumin and other proteins in the urine. The normal light microscopic appearance of the kidney in MCD further supports the diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Rarefaction of glomerular basement membrane is a feature of membranous nephropathy, not MCD.
**Option B:** Deposition of electron-dense material in the basement membrane is characteristic of membranous nephropathy or membranoproliferative glomerulonephritis.
**Option C:** Thin basement membrane is a feature of thin basement membrane disease, a different type of glomerulopathy.

**Clinical Pearl / High-Yield Fact**
The absence of significant hematuria and the presence of massive proteinuria in a patient with nephrotic syndrome should raise the suspicion of minimal change disease, which is often responsive to corticosteroid therapy.

**✓ Correct Answer: A. Fusion of foot processes of yhe glomerular epithelial cells**