The correct answer is option 2: Pellagra. Niacin, also known as vitamin B3, is an essential nutrient that is a part of the B complex group of vitamins. A deficiency of niacin can lead to a disease called pellagra. Pellagra is characterized by symptoms such as dermatitis, diarrhea, dementia, and in severe cases, death. The symptoms of pellagra occur due to the lack of niacin, which is necessary for the body to release energy from carbohydrates and maintain the health of the skin, digestive system, and nervous system. It is important to ensure an adequate intake of niacin through a balanced diet to prevent the development of pellagra.