The F$^-$ ions make the enamel on teeth much harder by converting hydroxyapatite (the enamel on the surface of teeth) into much harder fluoroapatite having the formula:
- [3(Ca$_3$(PO$_4$)$_2$).CaF$_2$]
- [3(Ca$_2$(PO$_4$)$_2$).Ca(OH)$_2$]
- [3(Ca$_3$(PO$_4$)$_3$.CaF$_2$]
- [3(Ca$_3$(PO$_4$)$_2$.Ca(OH)$_2$]
The Correct Option is A
Solution and Explanation
Explanation:
- Hydroxyapatite, [Ca5(PO4)3(OH)], is present in tooth enamel.
- When fluoride ions (F−) are introduced, they replace the hydroxide ions (OH−), forming fluoroapatite:
Ca5(PO4)3(OH) + F− → Ca5(PO4)3F.
- Fluoroapatite has the molecular formula [3(Ca3(PO4)2·CaF2)], which is harder and more resistant to decay.
Final Answer: Option (1).
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