Final answer:
Fluorosis in teeth and skeletal fluorosis are indicators of excessive fluoride intake, which is toxicity from fluoride. This can happen in areas with high fluoride levels in groundwater.
Step-by-step explanation:
Fluorosis in teeth and skeletal fluorosis are signs of fluoride toxicity. The correct answer is B. Fluoride. Fluoride ions help protect our teeth by reacting with hydroxylapatite in the teeth to form a less soluble substance called fluorapatite. However, excessive fluoride intake, which can occur in areas with naturally high levels of fluoride in groundwater, leads to dental and skeletal fluorosis, conditions that affect the teeth and bones, respectively. The World Health Organization (WHO) recognizes fluoride as one of the most serious inorganic contaminants in drinking water on a global basis.