**Core Concept**
Intrinsic Factor of Castle is a glycoprotein that plays a crucial role in vitamin B12 absorption. It is produced in the stomach and binds to dietary vitamin B12, facilitating its absorption in the terminal ileum.

**Why the Correct Answer is Right**
Intrinsic Factor of Castle is secreted by the parietal cells in the gastric glands. Parietal cells, also known as oxyntic cells, are responsible for producing hydrochloric acid (HCl) and intrinsic factor. The intrinsic factor binds to vitamin B12, protecting it from degradation and allowing it to be absorbed in the terminal ileum. This process is essential for maintaining adequate vitamin B12 levels in the body.

**Why Each Wrong Option is Incorrect**
**Option A:** Mucous cells are responsible for producing mucus, which protects the gastric mucosa from acid and enzymes. They do not produce intrinsic factor.
**Option B:** Chief cells, also known as peptic cells, produce pepsinogen, which is converted to pepsin, an enzyme that breaks down proteins in the stomach. They do not produce intrinsic factor.
**Option C:** G cells produce gastrin, a hormone that stimulates the secretion of gastric acid and pepsin. They do not produce intrinsic factor.

**Clinical Pearl / High-Yield Fact**
Pernicious anemia, a condition characterized by vitamin B12 deficiency, can be caused by autoimmune destruction of parietal cells, leading to a lack of intrinsic factor production.

**Correct Answer:** C. Parietal cells.