**Core Concept**
The absorption of Vitamin B12 involves a complex process that requires intrinsic factor, a glycoprotein produced by the parietal cells in the stomach. This process is essential for the proper utilization of Vitamin B12 in various bodily functions, including DNA synthesis and repair.

**Why the Correct Answer is Right**
Vitamin B12 is absorbed in the terminal ileum, a portion of the small intestine. The intrinsic factor binds to Vitamin B12 in the stomach and forms a complex that is resistant to gastric acid and pepsin. This complex is then transported to the terminal ileum, where the intrinsic factor-Vitamin B12 complex binds to a specific receptor on the surface of enterocytes, facilitating the absorption of Vitamin B12 into the bloodstream.

**Why Each Wrong Option is Incorrect**
**Option A:** The stomach is not the primary site of Vitamin B12 absorption. While Vitamin B12 is bound to intrinsic factor in the stomach, the actual absorption occurs in the small intestine.
**Option B:** The duodenum is the first portion of the small intestine, but it is not the primary site of Vitamin B12 absorption. The intrinsic factor-Vitamin B12 complex must be transported to the terminal ileum for absorption.
**Option C:** The jejunum is the middle portion of the small intestine, but it is not the primary site of Vitamin B12 absorption. The intrinsic factor-Vitamin B12 complex must be transported to the terminal ileum for absorption.

**Clinical Pearl / High-Yield Fact**
Intrinsic factor deficiency, as seen in pernicious anemia, can lead to Vitamin B12 deficiency, resulting in megaloblastic anemia, neurological symptoms, and increased risk of cardiovascular disease.

**Correct Answer: D. Terminal ileum**