A dental disease characterised by mottling of teeth is due to the presence of certain chemical element in drinking water. Which of the following is that element?

Options

A. Fluorine
B. Boron
C. Mercury
D. Chlorine

Explanation

To solve the question regarding the dental disease characterized by mottling of teeth due to a chemical element in drinking water, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a chemical element that causes a dental disease characterized by mottling of teeth. This condition is often associated with the consumption of contaminated drinking water.

2. **Identify the Options**: The options provided are:
- Fluorine
- Boron
- Mercury
- Chlorine

3. **Recall Relevant Information**:
- Mottling of teeth is a condition that can occur due to excessive intake of certain substances.
- Fluorine, when present in high concentrations in drinking water, is known to cause dental fluorosis, which leads to mottling and discoloration of teeth.

4. **Analyze Each Option**:
- **Fluorine**: Known to cause dental fluorosis when present in excess in drinking water.
- **Boron**: Not typically associated with dental mottling.
- **Mercury**: Associated with other health issues but not specifically with mottling of teeth.
- **Chlorine**: Used for water purification, not linked to dental mottling.

5. **Conclusion**: Based on the analysis, the correct answer is Fluorine, as it is the chemical element that causes mottling of teeth due to its excessive presence in drinking water.

### Final Answer:
**Fluorine**

---