## **Core Concept**
The optimal level of fluoride in drinking water for prevention of dental caries is a well-established public health measure. Fluoride helps in the prevention of dental caries by making teeth more resistant to acid attacks from plaque bacteria and sugars in the mouth.

## **Why the Correct Answer is Right**
The correct level of fluoride in water to prevent caries is around 0.5-1.5 mg/L, but the most commonly recommended level is **1 mg/L**. This concentration is considered optimal because it provides protection against dental caries without causing dental or skeletal fluorosis. The mechanism involves the substitution of fluoride for hydroxide ions in the hydroxyapatite crystal structure of tooth enamel, making teeth more resistant to acid dissolution.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 0.1 mg/L is too low to provide significant protection against dental caries.
- **Option B:** 5 mg/L is higher than the recommended level and could potentially lead to dental or skeletal fluorosis.
- **Option D:** 10 mg/L is much higher than the recommended level and increases the risk of fluorosis significantly.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the optimal fluoride level in drinking water can vary slightly based on climate and oral health status of the population. However, **1 mg/L** is a commonly accepted standard globally for the prevention of dental caries.

## **Correct Answer Line**
**Correct Answer: C. 1.**