Q: Fluoride ion is widely used in water supplies to help prevent what?


Read this paragraph and choose the correct option from the provided answers:

Fluoride ion is widely used in water supplies to help prevent tooth decay. Chloride is an important component in ion balance in blood. Iodide ion is needed by the thyroid gland to make the hormone thyroxine.

 Choices:

- rust

- bacteria

- chlorine taste

- tooth decay


A:
tooth decay