Why does much of the nation drink fluoridated water? What will be an ideal response?
The fluoride ion dissolved in water reduces the incidence of tooth cavities when it is present in
amounts of 1.0 to 1.5 ppm. Tooth enamel and bone are composed of the mineral apatite, whose
structure allows the free substitution of fluoride, chloride, or hydroxyl ions in the mineral structure. In
the presence of fluoride, the crystals of apatite in tooth enamel are larger and more perfect, which
makes them resist decay. Too much fluoride in drinking water, however—concentrations greater than
4 ppm—can cause children’s teeth to become mottled with dark spots. It took decades and many
studies to prove that fluoride is an effective way to dramatically reduce tooth decay.
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Mantle plumes are found primarily at:
a. divergent plate boundaries. b. convergent plate boundaries. c. transform plate boundaries. d. intraplate regions. e. none of the above
If an air parcel is given a small push upward and it falls back to its original position, the atmosphere is said to be ____
A) stable B) unstable C) isothermal D) adiabatic
The North Atlantic Drift is a warm current
Indicate whether the statement is true or false
Why are raindrops larger than 5 millimeters rare?
A) Because they start as snowflakes, they must grow much larger than 5 millimeters while falling from a cloud without sublimating. B) If they form larger than 5 millimeters then they will reach the ground as snow or hail instead of rain because they cannot melt completely. C) The frictional drag from falling is greater than the surface tension that holds the drops together when they get larger than 5 millimeters. D) There is no process to form large raindrops in clouds.