## Core Concept
Defluoridation refers to the process of removing excess fluoride from water to prevent fluorosis, a condition caused by excessive intake of fluoride. Various methods can be employed for defluoridation, including chemical and physical treatments.

## Why the Correct Answer is Right
The correct answer, ., involves the use of **Nalumite** or **Activated Alumina** which are commonly used for defluoridation. These materials have a high affinity for fluoride ions and can effectively remove them from water through an ion exchange process.

## Why Each Wrong Option is Incorrect
* **Option A:** - This option does not represent a recognized method for defluoridation.
* **Option B:** - This option might relate to a different water treatment process but is not specifically used for defluoridation.
* **Option C:** - Similarly, this option does not correspond to a known defluoridation technique.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **excessive fluoride consumption** can lead to **skeletal fluorosis** and **dental fluorosis**. Defluoridation methods like using **Activated Alumina** or **Nalumite** are crucial in regions with high fluoride levels in groundwater.

## Correct Answer Line
**Correct Answer: D. .**