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Fluoride in drinking water is considered desirable up to about 1 ppm because fluoride helps harden tooth enamel by transforming [3Ca3(PO4)2.Ca(OH)2] into which compound?

1. [CaF2]
2. [3(CaF2).Ca(OH)2]
3. [3(Ca3(PO4)2.CaF2]
4. [3{(Ca(OH)2.CaF2]

Correct answer: [3(Ca3(PO4)2.CaF2]

Solution

Fluoride enhances the strength of tooth enamel by replacing hydroxide ions in hydroxyapatite, which is represented by the formula [3(Ca3(PO4)2.CaF2], thus forming a more resilient compound that helps prevent cavities.

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