## Core Concept
Seliwanoff's test is a chemical test used to distinguish between **aldoses** and **ketoses**, which are types of monosaccharides. This test is based on the dehydration of sugars to form **5-hydroxymethylfurfural** and its derivatives, which then react with resorcinol to produce a red-colored compound.

## Why the Correct Answer is Right
The correct answer, **D. Fructose**, is a ketohexose, and Seliwanoff's test is positive for ketoses. When fructose is heated with hydrochloric acid, it rapidly dehydrates to form 5-hydroxymethylfurfural, which then reacts with resorcinol present in the test solution to produce a red-colored compound. This reaction is characteristic of ketoses, making the test positive for fructose.

## Why Each Wrong Option is Incorrect
* **Option A:** Glucose is an aldose, not a ketose. Therefore, it does not give a positive Seliwanoff's test.
* **Option B:** Lactose is a disaccharide composed of glucose and galactose. While it can hydrolyze into these monosaccharides, it does not directly give a positive Seliwanoff's test because it is not a ketose.
* **Option C:** Sucrose is a disaccharide made of glucose and fructose. Although it contains a ketose (fructose), the test is typically performed on monosaccharides or compounds that can easily hydrolyze to monosaccharides. Sucrose does not directly yield a positive result because the glycosidic bonds need to be hydrolyzed first.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Seliwanoff's test can be used to detect the presence of **ketoses** in a solution. Clinically, this can be relevant in the context of diagnosing certain metabolic disorders or in distinguishing between different types of sugars.

## Correct Answer: D. Fructose