**Core Concept**
The Glycemic Index (GI) is a measure of the rate at which the blood glucose levels rise after consuming a particular food item. It is an important factor in managing diabetes and is used to categorize food into high, medium, and low GI groups.

**Why the Correct Answer is Right**
The correct answer is **Glucose** because it is a simple sugar that is rapidly absorbed into the bloodstream, causing a significant and rapid increase in blood glucose levels. Glucose has a GI value of 100, which is the reference point for all other foods. The high GI value of glucose makes it the correct answer. The rapid absorption of glucose triggers a rapid increase in insulin secretion, which can lead to a rapid increase in blood glucose levels.

**Why Each Wrong Option is Incorrect**
* **Option A:** **White Bread** has a relatively low GI value of around 70, which is lower than glucose due to its slower digestion and absorption rate.
* **Option B:** **Brown Rice** has a GI value of around 50, which is lower than glucose due to its slower digestion and absorption rate.
* **Option C:** **Banana** has a GI value of around 55, which is lower than glucose due to its slower digestion and absorption rate.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the GI value of food can vary depending on the ripeness, cooking, and processing of the food item. Therefore, it's crucial to consult the GI value of specific food items to make informed dietary choices.

**Correct Answer:** D. Glucose