Which contaminant is found in groundwater due to dissolution from geological formations and can cause dental fluorosis?

Fluoride is a naturally occurring mineral often found in geological formations. When groundwater passes through these formations, it can dissolve fluoride, leading to increased concentrations in the water supply. This high level of fluoride can lead to dental fluorosis, a condition that results from excessive fluoride exposure during the early years of tooth development, causing discoloration and mottling of the enamel.

In contrast, nitrogen, iron, and manganese are also present in groundwater but are associated with different issues. Nitrogen, typically in the form of nitrates, is mainly a concern for its impact on water quality and human health, particularly in relation to agricultural runoff. Iron can stain water and laundry but does not have the same dental effects as fluoride. Manganese can affect the taste of water and impart a brownish color but does not cause dental fluorosis either. Thus, the link between fluoride and dental fluorosis makes it the correct answer to this question.