A reducing agent is typically used to treat which substance?

A reducing agent plays a significant role in chemical processes, particularly in the treatment of certain heavy metals in wastewater. In this context, chromium is commonly treated using a reducing agent because it often exists in the hexavalent form (Cr(VI)), which is highly toxic and soluble. The goal of using a reducing agent is to convert hexavalent chromium into its trivalent form (Cr(III)), which is much less toxic and more stable in wastewater treatments.

This reduction process typically involves adding agents like ferrous ion or sulfides that help to effectively neutralize the harmful effects of chromium in the environment. By reducing the oxidation state of chromium, the treatment process helps to mitigate the risks posed by discharge into water bodies or soil.

In contrast, while mercury, lead, and arsenic can also present serious environmental health concerns, they are treated through different chemical processes and methods. For instance, mercury may be treated by precipitation or by complexation, whereas lead often involves stabilization or immobilization techniques. Arsenic can also be treated using various techniques, including adsorption or precipitation, depending on its form in the wastewater.

Therefore, using a reducing agent specifically aligns with the treatment needs associated with chromium's toxic hexavalent state, making chromium the correct choice