Q45. 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.\\
(1) $\left[ 3 \left( \mathrm { Ca } _ { 3 } \left( \mathrm { PO } _ { 4 } \right) _ { 2 } \right) \cdot \mathrm { Ca } ( \mathrm { OH } ) _ { 2 } \right]$\\
(2) $\left[ 3 \left( \mathrm { Ca } _ { 3 } \left( \mathrm { PO } _ { 4 } \right) _ { 3 } \right) \cdot \mathrm { CaF } _ { 2 } \right]$\\
(3) $\left[ 3 \left( \mathrm { Ca } _ { 2 } \left( \mathrm { PO } _ { 4 } \right) _ { 2 } \right) \cdot \mathrm { Ca } ( \mathrm { OH } ) _ { 2 } \right]$\\
(4) $\left[ 3 \left( \mathrm { Ca } _ { 3 } \left( \mathrm { PO } _ { 4 } \right) _ { 2 } \right) \cdot \mathrm { CaF } _ { 2 } \right]$