The recommended concentration of fluoride ion in drinking water

Question:

The recommended concentration of fluoride ion in drinking water is up to 1 ppm as fluoride ion is required to make teeth enamel harder by converting $\left[3 \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} \cdot \mathrm{Ca}(\mathrm{OH})_{2}\right]$ to :

  1. $\left[3\left(\mathrm{CaF}_{2}\right) \cdot \mathrm{Ca}(\mathrm{OH})_{2}\right]$

  2. $\left[3\left(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} \cdot \mathrm{CaF}_{2}\right]\right.$

  3. $\left[3\left(\mathrm{Ca}(\mathrm{OH})_{2}\right] \cdot \mathrm{CaF}_{2}\right]$

  4. $\left[\mathrm{CaF}_{2}\right]$


Correct Option: , 2

Solution:

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