## Core Concept
Nephrotic syndrome is characterized by heavy proteinuria (>3.5 g/1.73 m²/24 hr), hypoalbuminemia, hyperlipidemia, and edema. The condition results from damage to the glomeruli, leading to loss of plasma proteins, including albumin and antithrombin III (AT-III), in the urine.

## Why the Correct Answer is Right
The correct answer involves understanding the pathophysiological changes in nephrotic syndrome.
- **Low serum calcium (a)**: This is correct because hypoalbuminemia leads to low total serum calcium levels, although ionized calcium levels may be normal.
- **Low lipid (c)**: This option is incorrect in the context of nephrotic syndrome, where hyperlipidemia is commonly observed due to increased hepatic synthesis of lipids in response to hypoalbuminemia.
- **Raised AT-III (b)**: This is incorrect because nephrotic syndrome is associated with decreased levels of AT-III due to urinary loss, which contributes to a hypercoagulable state.
- **Platelet activation (d)**: This is seen in nephrotic syndrome, partly due to the loss of anticoagulant proteins like AT-III and increased levels of clotting factors.

## Why Each Wrong Option is Incorrect
- **Option B: Raised AT-III**: Incorrect because AT-III levels are decreased in nephrotic syndrome, not raised, contributing to a prothrombotic state.
- **Option C: Low lipid**: Incorrect because nephrotic syndrome is characterized by hyperlipidemia, not low lipid levels.
- **Option D does not need explanation as it is part of a correct combination**

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that patients with nephrotic syndrome are at increased risk of thrombosis due to the loss of AT-III and other anticoagulant proteins in the urine. This risk is significant and can be a presenting feature or complication of the disease.

## Correct Answer: D.