## **Core Concept**
The use of fluoridated salt is a public health measure aimed at reducing dental caries. Fluoride, when ingested in appropriate amounts, can help strengthen tooth enamel and make teeth more resistant to decay. The optimal amount of fluoride in salt for caries reduction needs to be balanced to provide benefits while minimizing risks of dental or skeletal fluorosis.

## **Why the Correct Answer is Right**
The correct answer of **250 ppm (parts per million)** is based on research indicating that this concentration of fluoride in salt effectively reduces dental caries without significantly increasing the risk of fluorosis. The World Health Organization and other health institutions have recommended such levels for community-based fluoride supplementation programs through salt.

## **Why Each Wrong Option is Incorrect**
- **Option A: 100 ppm** - This concentration is lower than the recommended minimum for effective caries reduction. It might not provide sufficient protection against dental caries.
- **Option B: 350 ppm** - While higher concentrations may offer greater protection, they also increase the risk of dental fluorosis and other adverse effects. The minimum effective dose is preferred to balance benefits and risks.
- **Option D: 500 ppm** - This is significantly higher than the minimum required and could increase the risk of adverse effects such as dental or skeletal fluorosis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the optimal level of fluoride in drinking water for caries prevention is **0.5-1.5 mg/L (or ppm)**, but for salt, the concentration needs to be much higher due to differences in consumption patterns. The use of fluoridated salt is particularly beneficial in areas where access to fluoridated water is limited.

## **Correct Answer: C. 250 ppm.**