**Core Concept**
Rothera's test is a chemical test used to detect the presence of reducing substances, particularly glucose, in biological fluids. This test relies on the reaction between the reducing substance and a reagent containing arsenite and sulfuric acid, resulting in the formation of a purple-colored compound.

**Why the Correct Answer is Right**
The correct answer to this question is glucose. Glucose is a reducing sugar that reacts with the reagent in Rothera's test to produce a purple-colored compound. This reaction occurs due to the oxidation of the glucose molecule, which is facilitated by the presence of arsenite and sulfuric acid in the reagent. The resulting compound is a characteristic purple color, indicating the presence of glucose.

**Why Each Wrong Option is Incorrect**
**Option A:** None of the other options are correct, as Rothera's test is specifically used to detect glucose and other reducing sugars.

**Option B:** This option is incorrect, as Rothera's test is not used to detect ketones. Ketone detection is typically performed using other methods, such as nitroprusside test.

**Option C:** This option is incorrect, as Rothera's test is not used to detect amino acids. Amino acid detection is typically performed using other methods, such as ninhydrin test.

**Clinical Pearl / High-Yield Fact**
Rothera's test is an important diagnostic tool in clinical settings, particularly in the diagnosis of diabetes mellitus. It is a simple and cost-effective method for detecting glucose in urine, which can aid in the early diagnosis and management of this condition.

**Correct Answer: D. Glucose**