JEE MAIN - Chemistry (2024 - 9th April Morning Shift - No. 6)
The $$\mathrm{F}^{-}$$ 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.
$$\left[3\left(\mathrm{Ca}_3\left(\mathrm{PO}_4\right)_2\right) \cdot \mathrm{CaF}_2\right]$$
$$\left[3\left(\mathrm{Ca}_3\left(\mathrm{PO}_4\right)_2\right) \cdot \mathrm{Ca}(\mathrm{OH})_2\right]$$
$$\left[3\left(\mathrm{Ca}_3\left(\mathrm{PO}_4\right)_3\right) \cdot \mathrm{CaF}_2\right]$$
$$\left[3\left(\mathrm{Ca}_2\left(\mathrm{PO}_4\right)_2\right) \cdot \mathrm{Ca}(\mathrm{OH})_2\right]$$
Explanation
Hydroxyapatite : $$\left[3\left(\mathrm{Ca}_3\left(\mathrm{PO}_4\right)_2\right) \cdot \mathrm{Ca}(\mathrm{OH})_2\right]$$
Fluoroapatite : $$\left[3\left(\mathrm{Ca}_3\left(\mathrm{PO}_4\right)_2\right) \cdot \mathrm{CaF}_2\right]$$
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