**Core Concept**
The concentration of fluoride in community water supplies is a critical public health measure to prevent dental caries while minimizing the risk of dental fluorosis. The optimal fluoride concentration is a balance between these two competing goals.

**Why the Correct Answer is Right**
The World Health Organization (WHO) proposed a fluoride concentration of 1 mg/L (1 ppm) in community water supplies in 1969. This concentration is based on evidence that it effectively reduces dental caries by 50-70% without causing significant dental fluorosis. The optimal fluoride concentration is thought to occur when the fluoride ion concentration in saliva is around 0.05-0.1 mg/L, which corresponds to a water concentration of approximately 1 mg/L.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a fluoride concentration of 0.5 mg/L is too low to have a significant impact on dental caries prevention.
* **Option B:** This option is incorrect because a fluoride concentration of 2 mg/L is associated with an increased risk of dental fluorosis, particularly in children.
* **Option C:** This option is incorrect because a fluoride concentration of 5 mg/L is excessively high and can cause severe dental fluorosis and other health problems.

**Clinical Pearl / High-Yield Fact**
The "optimal" fluoride concentration is not static and may vary depending on the local water chemistry, diet, and population demographics. It's essential to regularly monitor and adjust the fluoride concentration in community water supplies to maintain an optimal balance between caries prevention and dental health.

**Correct Answer:** B. 1 mg/L