**Core Concept**
Rothera's test is a chemical test used to detect the presence of **ketone bodies** in a patient's urine. It is based on the reaction of ketone bodies with a reagent containing **sodium nitroprusside**. This test is relevant in the diagnosis and management of **diabetic ketoacidosis**.

**Why the Correct Answer is Right**
The correct answer is related to the detection of **ketone bodies**, which are produced when the body breaks down **fatty acids** for energy instead of **glucose**. In diabetic ketoacidosis, the lack of **insulin** leads to an increase in **glucagon**, causing the liver to produce more **ketone bodies**. Rothera's test detects these ketone bodies, specifically **acetoacetic acid** and **acetone**, by reacting them with **sodium nitroprusside** to form a purple-colored compound.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Rothera's test is not primarily used for detecting **glucose** in urine, which is typically done with **dipstick tests**.
**Option B:** This option is incorrect as it is not related to the detection of ketone bodies.
**Option C:** This option is incorrect because it does not pertain to the chemical detection of ketone bodies in urine.

**Clinical Pearl / High-Yield Fact**
Rothera's test is a crucial tool in diagnosing and monitoring **diabetic ketoacidosis**, a life-threatening complication of **diabetes mellitus**. It is essential to remember that the presence of ketone bodies in the urine indicates a need for immediate medical attention.

**Correct Answer:** D. Ketone bodies.