Question

The enamel present on teeth becomes much harder due to the conversion of hydroxyapatite into fluorapatite. What are \( X \) and \( Y \)?

• A. \( X = {Ca(OH)}_2, Y = {CaF}_2 \)
• B. \( X = {Ca(OH)}_2, Y = {CaCl}_2 \)
• C. \( X = {Ca(OH)}_2, Y = {NaCl} \)
• D. \( X = {CaO}, Y = {CaCl}_2 \)

Hint:

Fluoride strengthens enamel by converting hydroxyapatite into fluorapatite.

Answer 1

The Correct Option is A

Step 1: Understanding Tooth Enamel Hardening
- Hydroxyapatite: \( {Ca}_5({PO}_4)_3{OH} \)
- Fluoride treatment replaces OH⁻ with F⁻, forming fluorapatite, which is stronger.
\[ 3{Ca}_5({PO}_4)_3{OH} + F^- \rightarrow 3{Ca}_5({PO}_4)_3{F} \]
- \( X = {Ca(OH)}_2 \) contributes OH⁻.
- \( Y = {CaF}_2 \) provides F⁻.