Final answer:
The correct concentration of fluoride in a municipal water supply to reduce caries without causing fluorosis is 1.0 ppm. At this concentration, an average person would ingest 1.92 mg of fluoride ion daily if they drink 1,920 mL of water.
Step-by-step explanation:
The concentration of fluoride in a municipal water supply that is required to significantly reduce the caries incidence without causing dental fluorosis is 1.0 ppm (part per million). The World Health Organization recommends this as the maximum fluoride ion concentration in drinking water. Therefore, the correct answer is B. 1.0ppm. If an average person drinks 1,920 mL of water per day with this concentration, they would be ingesting 1.92 milligrams of fluoride ion. It's worth noting that the maximum safe level of fluoride ion in tap water identified by the EPA is 4 ppm, although higher concentrations in products such as toothpaste show greater effectiveness in preventing tooth decay.