Fluorine pollution mainly affects
A. Brain
B. Heart
C. Teeth
D. Kidney

Hint: Fluorine, in moderation, helps to maintain the structure of bones and similar tissues. Fluorine is a very common element. The element acts in the form of fluoride ions. The fluorides are present in the earth’s crust abundantly. It is also present in abundance in natural water and food sources. Find the option which is closer in structure to that of a bone.

Complete answer:
Fluorine helps in the development of bones, the enamel of the teeth, and thyroid glands.
The way it is fighting off cavities producing microbes or acidity is by combining itself with phosphorus and calcium ions in the tooth enamel. This will result in the production of fluorapatite, a phosphate compound in the form of a strong crystalline solid. But this works only in moderation.
The bioavailability of natural fluoride is found to be around ninety percent. This means that almost all of the naturally injected fluoride is giving out fluorine to the body sufficiently. This is where fluorine pollution comes in.
The increase in the amount of fluorine taken up by the body results in deterioration of the enamel known as fluorosis. The excess fluorine present will replace the calcium ions in the bones and teeth, making it very brittle and vulnerable to acidity attacks. An increase in the amount of fluoride uptake in kids is shown to have deleterious effects in bones and teeth.
Fluorine pollution mainly affects teeth.

Note:
Water fluoridation has occurred in many developing countries as an act to improve dental health. Nowadays many toothpaste companies are also including fluoride in their product. Remembering this can be a dead give away of the answer.