## **Core Concept**
The question tests knowledge of parasitology, specifically the concentration techniques used for recovering eggs or larvae of various parasites from stool samples. A saturated salt solution (also known as a flotation solution) is commonly used for this purpose. Different parasites have varying densities, which affect their ability to float in such solutions.

## **Why the Correct Answer is Right**
The correct answer, **D. Schistosoma**, is right because Schistosoma eggs do not typically concentrate in a saturated salt solution. This is due to their relatively high density compared to the flotation solution. Schistosoma eggs are usually recovered through other methods, such as sedimentation techniques.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *Ascaris* eggs can indeed be concentrated using a saturated salt solution because they are less dense than the solution, allowing them to float.
- **Option B:** *Trichuris* (whipworm) eggs also float in a saturated salt solution due to their low density, making them recoverable through this method.
- **Option C:** *Hookworm* eggs similarly can be concentrated using this technique as they too are less dense than the saturated salt solution.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while a saturated salt solution is effective for concentrating eggs of many helminths, it may not be suitable for all. For example, *Schistosoma* eggs are best recovered by examining a wet mount of stool or using a sedimentation technique. This highlights the importance of choosing the right concentration method based on the suspected parasite.

## **Correct Answer:** . Schistosoma