Which of the following are commonly used coagulation chemicals?

Coagulation is a critical process in water treatment that involves the addition of chemicals to help aggregate suspended particles into larger flocs, which can then be easily removed from the water. Among the common coagulation chemicals, alum (aluminum sulfate) is widely utilized due to its effectiveness in neutralizing charges of suspended particles, allowing them to clump together. Metallic salts like ferric chloride and ferric sulfate also serve the same purpose and are recognized as traditional coagulants.

In addition to alum and metallic salts, polymers can also be used in the coagulation process. These are often referred to as coagulant aids, as they enhance the coagulation process by helping to form larger floc particles and improving the settling process. These polymers can be particularly useful in water with low turbidity or when an additional boost to floc formation is needed.

This understanding emphasizes that the combination of these groups of chemicals is standard practice in coagulation treatment, making the selection that includes both alum and metallic salts along with polymers the correct choice. Thus, the answer correctly identifies both commonly used coagulation chemicals and reinforces the diverse approaches water treatment professionals take to ensure effective water purification.