Which one of the following elemental forms is not present in the enamel of the teeth ?

Options

A. `Ca^(2+)`
B. `P^(3+)`
C. `F^(-)`
D. `P^(5+)`

Answer

To determine which elemental form is not present in the enamel of teeth, we need to analyze the composition of tooth enamel. Tooth enamel is primarily made up of a mineral called hydroxyapatite, which has the chemical formula Ca10(PO4)6(OH)2.

### Step-by-Step Solution:

1. **Identify the Main Components of Enamel**:
- Tooth enamel is primarily composed of hydroxyapatite, which contains calcium (Ca), phosphorus (P), and oxygen (O).

2. **Understanding Hydroxyapatite**:
- Hydroxyapatite can be represented as Ca10(PO4)6(OH)2. This shows that it contains calcium ions (Ca²⁺), phosphate ions (PO4³⁻), and hydroxide ions (OH⁻).

3. **Role of Fluoride in Enamel**:
- Fluoride ions (F⁻) can replace hydroxide ions in hydroxyapatite to form fluorapatite (Ca10(PO4)6F2), which is a harder form of enamel. This indicates that fluoride is also a component of enamel.

4. **Consider Other Elements**:
- The question asks for an elemental form that is not present in the enamel. We have established that calcium, phosphorus, oxygen, and fluoride are present.

5. **Identify the Element Not Present**:
- Common elements that might be considered include metals like iron (Fe), magnesium (Mg), and others. Among these, iron is not a component of tooth enamel.

### Conclusion:
The elemental form that is not present in the enamel of teeth is **iron (Fe)**.