Which of the following is a possible contact chemical used in water treatment?

In water treatment processes, the term "contact chemical" refers to substances that are intentionally added to water to achieve specific treatment goals. Each of the substances listed serves important purposes in improving water quality.

Alum, or aluminum sulfate, is commonly used as a coagulant. When added to water, it helps to aggregate and remove particulates, resulting in clearer water. Its effectiveness in coagulating impurities makes it invaluable in various treatment applications.

Chlorine is one of the most widely used disinfectants in water treatment. It effectively kills bacteria, viruses, and other pathogens, ensuring that drinking water is safe for consumption. The contact time between chlorine and water is critical for achieving adequate disinfection, hence it fits the definition of a contact chemical.

Potassium permanganate is another versatile chemical used in water treatment. It serves as an oxidizing agent and is effective in controlling taste and odor, as well as in removing iron and manganese from water. Its strong oxidizing properties make it beneficial for treating contaminated water supplies.

Given that alum, chlorine, and potassium permanganate are all used in water treatment for different purposes, it is accurate to recognize that each of these substances qualifies as a contact chemical. Thus, the correct answer encompasses all three options