The standard coagulant in water treatment is:

Concept

Coagulation destabilizes fine suspended and colloidal particles that do not settle readily on their own. A coagulant produces charged hydrolysis products and gelatinous flocs; these neutralize particle charges, capture impurities, and permit later settling or filtration.

Application

Alum—commonly aluminium sulfate—is widely used because, under suitable pH and alkalinity, it forms aluminium hydroxide flocs that sweep suspended matter from water.

Contrast

• Hypochlorite releases active chlorine through aqueous equilibria and is chiefly associated with oxidation and disinfection.

• Chlorine is chiefly used to inactivate microorganisms and maintain a disinfectant residual.

• Metallic aluminium is not dosed directly; water-treatment coagulants use soluble aluminium salts.

• Alum supplies soluble aluminium species that hydrolyse and build particle-trapping flocs.

Result

Therefore, the standard coagulant among the given values is Alum.