Question

Assertion : Soluble fluoride is often added to drinking water to bring its concentration up to $1\, ppm$.
Reason : $F^{-}$ ion concentration above $2 \,ppm$ causes brown mottling of teeth.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

$F^{-}$ ions make the enamel on teeth much harder by converting hydroxyapatite, $[3(Ca_{3}(PO_{4} )_{2}) \cdot Ca(OH)_{2}]$, the enamel on the surface of the teeth, into much harder fluorapatite $[3(Ca_{3}(PO_{4})_{2})\cdot CaF_{2}]$.