According to international standards of drinking water, the tolerable limit for fluoride ions in water is ______

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the tolerable limit of fluoride ions in drinking water according to international standards.

2. **Researching International Standards**: According to various health organizations and international standards, the tolerable limit for fluoride ions in drinking water is established to ensure safety and health.

3. **Identifying the Tolerable Limit**: The recognized tolerable limit for fluoride ions in drinking water is **1 part per million (ppm)**. This level is considered safe and beneficial for dental health as it helps in the formation of strong enamel.

4. **Consequences of Exceeding the Limit**: It is important to note that if the fluoride concentration exceeds 2 ppm, it can lead to dental issues such as brown mottling of teeth. At concentrations above 10 ppm, it can cause more severe health problems affecting bones and teeth.

5. **Final Answer**: Therefore, according to international standards, the tolerable limit for fluoride ions in water is **1 part per million (ppm)**.

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