The recommended concentration of fluoride ion in drinking water is up to 1 ppm as fluoride ion is required to make teen enamel harder by converting `[3Ca_(3) (PO_(4))_(2). Ca(OH)_(2)]` to :

Options

A. `[CaF_(2)]`
B. `[3 (CaF_(2)). Ca(OH)_(2)]`
C. `[3Ca_(3) (PO_(4))_(2). CaF_(2)]`
D. `[3 {(Ca(OH)_(2)}.CaF_(2)]`

Explanation

To solve the question regarding the conversion of hydroxyapatite to fluorapatite due to the presence of fluoride ions, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Chemical Composition**:
The chemical formula provided is `[3Ca_(3)(PO_(4))_(2)·Ca(OH)_(2)]`, which represents hydroxyapatite, a mineral form of calcium apatite that is a primary component of tooth enamel.

2. **Understand the Role of Fluoride Ion**:
The fluoride ion (F⁻) is known to enhance the hardness of tooth enamel. It does this by replacing hydroxide ions (OH⁻) in hydroxyapatite.

3. **Write the Reaction**:
The fluoride ion reacts with hydroxyapatite to form fluorapatite. The reaction can be represented as:
\[ 3Ca_3(PO_4)_2·Ca(OH)_2 + F^- \rightarrow 3Ca_3(PO_4)_2·CaF_2 \]
Here, the hydroxide ions are replaced by fluoride ions.

4. **Identify the Product**:
The product formed from this reaction is fluorapatite, which has the formula `Ca_3(PO_4)_2·CaF_2`. This compound is harder and more resistant to acid than hydroxyapatite.

5. **Conclusion**:
Thus, the fluoride ion converts hydroxyapatite into fluorapatite, which is beneficial for dental health.

### Final Answer:
The fluoride ion converts `[3Ca_(3)(PO_(4))_(2)·Ca(OH)_(2)]` to `Ca_3(PO_4)_2·CaF_2` (fluorapatite).

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