A. Iron: Iron supports oxygen transport via hemoglobin but is not directly involved in collagen synthesis or wound healing. B. Vitamin C: Vitamin C is essential for collagen synthesis and immune function, which are critical in wound healing, especially for wounds healing by secondary intention. C. Potassium: Potassium helps maintain cellular function but is not a primary nutrient involved in wound repair. D. Niacin: Niacin is important in energy metabolism but does not play a direct role in wound healing.