Chemistry - Environmental Chemistry Question with Solution | TestHub

The ${\mathrm{F}}^{\ominus }$ ions make the enamel on teeth much harder by converting hydroxyapatite. $[3\left({\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2\cdot \mathrm{Ca}(\mathrm{OH}{)}_2\right]$ into much harder fluorapatite.

[3 $\left({\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2\cdot {\mathrm{CaF}}_2\right]$ so deficiency of ${\mathrm{F}}^{\ominus }$ causes disease such as tooth decay.

${\mathrm{F}}^{\ominus }$ ion concentration above 2 ppm causes brown mottling of teeth.