**Core Concept**
Pellagra is a disease characterized by dermatitis, diarrhea, dementia, and potentially death, caused by a specific nutritional deficiency. This condition is closely linked to the metabolism of a particular amino acid found in many protein-rich foods.

**Why the Correct Answer is Right**
Pellagra is primarily caused by a deficiency of **Niacin** (Vitamin B3), which is essential for the synthesis of **NAD** and **NADP**. These coenzymes play a crucial role in energy metabolism, DNA repair, and other vital cellular processes. Without sufficient Niacin, the body cannot produce adequate amounts of these coenzymes, leading to the characteristic symptoms of pellagra. The condition is often seen in individuals consuming a diet heavily reliant on **maize** (corn), which lacks sufficient Niacin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Pellagra is not caused by a deficiency of **Vitamin B1 (Thiamine)**, which is essential for carbohydrate metabolism and the prevention of beriberi. While both conditions are caused by deficiencies in B vitamins, they are distinct and involve different nutritional deficiencies.

**Option B:** This option is incorrect because **Vitamin B2 (Riboflavin)** deficiency causes **Ariboflavinosis**, characterized by lesions of the skin, mucous membranes, and cornea, but does not lead to the symptoms of pellagra.

**Option C:** This option is incorrect because **Vitamin B6 (Pyridoxine)** deficiency can cause **Peripheral neuropathy**, **Seizures**, and other neurological symptoms, but does not cause pellagra.

**Clinical Pearl / High-Yield Fact**
Pellagra is often referred to as the "four Ds" disease: **Dermatitis**, **Diarrhea**, **Dementia**, and **Death**.

**Correct Answer: C. Vitamin B3 (Niacin)**