Which of the following chemicals is NOT used in water fluoridation?

The option indicating "none of the above" suggests that all the listed chemicals, sodium fluoride, sodium silicofluoride, and hydrofluosilic acid, are indeed used in water fluoridation. This is correct because water fluoridation utilizes various compounds to achieve optimal fluoride levels for dental health.

Sodium fluoride is a well-known fluoride compound frequently used to prevent dental cavities. Sodium silicofluoride is another fluoride compound that can be added to water supplies for the same purpose. Hydrofluosilic acid, which is derived from the scrubbing of industrial processes, is also a commonly used form of fluoride in water treatment.

In drinking water fluoridation practices, these compounds serve the essential function of reducing the incidence of tooth decay in the population by providing a controlled amount of fluoride. Therefore, since all listed chemicals are utilized in water fluoridation, selecting "none of the above" accurately reflects that statement.