The glycemic index for glucose is:

**Core Concept**
The glycemic index (GI) is a measure of how quickly a food raises blood glucose levels after consumption. It is a relative ranking of carbohydrate in foods based on their ability to raise blood sugar levels. The GI is expressed on a scale from 0 to 100, with pure glucose being the reference point at 100.

**Why the Correct Answer is Right**
Glucose is the standard reference point for the GI because it is rapidly absorbed and digested, causing a rapid increase in blood glucose levels. The GI of glucose is defined as 100, which means that a food with a GI of 100 will raise blood glucose levels at the same rate as pure glucose. This is because glucose is the most easily absorbed and digested carbohydrate, and its GI is used as a reference point to compare the GI of other carbohydrates.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not correctly state the GI of glucose. The GI of glucose is not 50, which would indicate a moderate rate of carbohydrate absorption and digestion.
* **Option B:** This option is incorrect because it does not correctly state the GI of glucose. The GI of glucose is not 200, which would indicate an extremely rapid rate of carbohydrate absorption and digestion.
* **Option C:** This option is incorrect because it does not correctly state the GI of glucose. The GI of glucose is not 0, which would indicate no increase in blood glucose levels.

**Clinical Pearl / High-Yield Fact**
The GI is an important consideration for patients with diabetes or those who are trying to manage their blood sugar levels. Foods with a high GI can cause a rapid increase in blood glucose levels, while foods with a low GI can help to slow down the digestion and absorption of carbohydrates.

**Correct Answer: B. 100**