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The presence of soluble fluoride ion upto 1 ppm concentration in drinking water, is -

1. harmful for teeth
2. harmful to bones
3. harmful to skin
4. safe for teeth

Correct answer: safe for teeth

Solution

About 1 ppm of soluble fluoride in drinking water is the recommended level; it strengthens enamel (as fluoroapatite) and prevents tooth decay, so it is safe for teeth. Harm (fluorosis) only occurs at much higher concentrations.

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