**Core Concept**
The formation of triglycerides in mucosal cells is a key aspect of lipid metabolism, particularly in the context of nutrient absorption and energy storage. This process involves the synthesis of triglycerides from fatty acids and glycerol, which is essential for maintaining energy homeostasis in the body.

**Why the Correct Answer is Right**
Triglycerides are formed primarily in the endoplasmic reticulum (ER) of mucosal cells, specifically in the enterocytes of the small intestine. This process involves the enzyme acyl-CoA:diacylglycerol acyltransferase (DGAT), which catalyzes the final step of triglyceride synthesis by transferring an acyl group from acyl-CoA to the 3-position of diacylglycerol. The resulting triglyceride is then packaged into chylomicrons and secreted into the lymphatic system for eventual delivery to the bloodstream.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a cellular location or a specific enzyme involved in triglyceride synthesis.
* **Option B:** This option is incorrect because it refers to a different type of cell, specifically adipocytes, which are involved in lipid storage rather than synthesis.
* **Option C:** This option is incorrect because it refers to a different cellular location, specifically the mitochondria, which is not the primary site of triglyceride synthesis in mucosal cells.

**Clinical Pearl / High-Yield Fact**
The synthesis of triglycerides in mucosal cells is a critical step in nutrient absorption and energy storage, and disruptions in this process can lead to disorders such as steatorrhea and malabsorption.

**Correct Answer: C. Endoplasmic reticulum (ER) of mucosal cells.**