## Core Concept
The Nalgonda technique is a public health intervention method used for the prevention of dental and skeletal fluorosis in regions with high fluoride levels in drinking water. This technique involves the adjustment of fluoride levels in drinking water to a safe range.

## Why the Correct Answer is Right
The Nalgonda technique specifically involves the addition of lime (calcium hydroxide) and alum (aluminum sulfate) to water to precipitate out excess fluoride, making the water safer for consumption. This method is particularly relevant in regions like Nalgonda district in Telangana, India, where high levels of fluoride in groundwater have been a significant public health concern. The technique effectively reduces fluoride levels, thereby preventing fluorosis.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately describe the Nalgonda technique.
- **Option B:** This option is incorrect as it is not related to the Nalgonda technique.
- **Option C:** This option might seem plausible but is incorrect because it does not specify the correct method for defluoridation of water.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the Nalgonda technique is specifically used for **defluoridation of water** to prevent **fluorosis**. This method is crucial in areas where the drinking water has high fluoride levels, posing a risk to public health.

## Correct Answer: D.