What is a common oxidant used in water chlorination?

Chlorine dioxide is a common oxidant used in water chlorination due to its effectiveness in disinfection and oxidation processes. It is particularly valued for its ability to eliminate bacteria, viruses, and protozoan cysts, making it a reliable choice in water treatment facilities. Chlorine dioxide also reacts with organic and inorganic materials, helping to control tastes, odors, and color in water, which enhances overall water quality.

The other options listed do not serve the same purpose as chlorination agents. Ammonium sulfate is primarily used as a fertilizer and does not play a role in water disinfection. Sand is often used in filtration processes but does not have oxidizing properties. Aluminum chloride is used as a coagulant in water treatment to aid in removing suspended particles, but it is not an oxidant like chlorine dioxide. Thus, chlorine dioxide stands out as a pivotal component in water chlorination, making it the correct choice.