Problem 17
What is the natural source of fluoride ion in water? How and why is the fluoride level in drinking water artificially increased to about \(1 \mathrm{ppm}\) in many municipalities? How can fluoride be removed from natural water in which its concentration is too high?
Problem 20
Explain why aluminum ion concentrations in acidified waters are much greater than those in neutral water. How does the increased aluminum ion level affect fish and trees?
