Final answer:
Fluoride is the compound that, when added to drinking water at a concentration of 1 ppm, prevents cavities by forming a less soluble fluorapatite in tooth enamel, enhancing resistance to acid attacks and inhibiting cavity-causing bacteria.
Step-by-step explanation:
Fluoride and Cavity Prevention
The compound that prevents cavities when added to drinking water at 1 ppm is fluoride. Fluoride ions from compounds such as sodium fluoride (NaF) or stannous fluoride (SnF₂) are added to public water supplies and toothpastes to bolster dental health by preventing tooth decay. Fluoride helps protect our teeth by reacting with the hydroxyapatite in tooth enamel to form fluorapatite, which is more resistant to acid attacks and therefore less soluble, safeguarding against cavities. This process of adding fluoride to drinking water is commonly referred to as fluoridation. The effectiveness of fluoride is attributed to its ability to become incorporated into tooth enamel, enhancing the enamel's resistance and also inhibiting the growth of bacteria responsible for cavity formation.
While other halogens such as chlorine, bromine, and iodine have their own uses in chemistry and biological functions, it is the fluoride ion that is known for its role in dental health. For example, chloride is vital for ion balance in blood, and iodide is essential for thyroid hormone production. However, only fluoride is recognized for its cavity-preventing properties when added to drinking water at low concentrations.