Which one of the following is a chemical treatment process of waste water treatment?

Neutralisation adjusts the pH of waste water by adding acid or alkali, a chemical reaction that changes the effluent's composition.

Sedimentation lets suspended solids settle out under gravity, a purely physical separation.

Aeration supplies oxygen to support microbial breakdown, working through physical and biological means.

Adsorption traps dissolved impurities on a solid surface such as activated carbon, a physical surface process.

Chemical treatments alter substances by reaction, unlike physical steps that only separate or transfer them.

Coagulation and disinfection with chlorine are other common chemical stages of waste water treatment.