Okay, let's tackle this question. The patient is a 7-year-old boy with generalized edema, albuminuria, hypoalbuminemia, and hyperlipidemia. These symptoms point towards nephrotic syndrome. Now, the kidney biopsy on light microscopy shows normal appearance. The question is about what electron microscopy would reveal.

First, I need to recall the different types of nephrotic syndrome in children. Minimal change disease (MCD) is the most common cause in children. MCD typically presents with normal light microscopy findings, but electron microscopy shows effacement of the foot processes of the podocytes. Other types like focal segmental glomerulosclerosis (FSGS) or membranous nephropathy would have different light microscopy findings. For example, FSGS might show segmental sclerosis under light microscopy, and membranous nephropathy would have subepithelial immune deposits visible with silver stains.

The options given are not listed, but the correct answer is likely related to MCD. Since the light microscopy is normal, the electron microscopy findings would be the key here. So, the correct answer should be the effacement of foot processes. The other options, such as mesangial deposits or subepithelial deposits, would be seen in other types like IgA nephropathy or membranous nephropathy, which would have abnormal light microscopy findings. Therefore, the electron microscopy in this case would show the effacement of podocyte foot processes, which is characteristic of MCD.

**Core Concept**
This question tests understanding of **nephrotic syndrome in children**, particularly **minimal change disease (MCD)**. The clinical triad of nephrotic syndrome (edema, hypoalbuminemia, hyperlipidemia) with **normal light microscopy** and **foot process effacement on electron microscopy** is hallmark of MCD.

**Why the Correct Answer is Right**
**Electron microscopy in minimal change disease** reveals **effacement of podocyte foot processes**. This loss of foot process polarity disrupts the glomerular filtration barrier, leading to massive albuminuria. Light microscopy appears normal because there is no inflammation or structural damage visible at this resolution. MCD is the most common cause of nephrotic syndrome in children, accounting for ~80% of cases.

**Why Each Wrong Option is Incorrect**
**Option A:** *Mesangial deposits* are seen in IgA nephropathy, which presents with hematuria, not nephrotic syndrome.
**Option B:** *Subepithelial humps* are characteristic of post-streptococcal glomerulonephritis, which causes acute nephritic syndrome.
**Option C:** *Subendothelial deposits* are seen in membranoproliferative glomerulonephritis, which has abnormal light microscopy with double contours.
**Option D:** *Mesangial proliferation* is typical of focal segmental glomerulosclerosis (FSGS) or IgA nephropathy, both of which show abnormalities on light microscopy.

**Clinical Pearl / High-Yield Fact**
Remember the **"3 Ns"** of minimal change disease: **Nephrotic**, **Normal on light microscopy**, and **No immune complex deposits**. Always associate effacement of foot processes under electron microscopy with MCD in pediatric nephrotic syndrome.

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