Coagulation aid is a chemical which when used along with the main coagulant improves or accelerates the process of coagulation and flocculation by producing quick forming dense and rapid settling flocs.
With their use, the water purification capacity of the plant is increased as the rate of coagulation is increased.
Finely divided clay, bentonites and activated powdered carbon are the most commonly used materials as nuclei to floc formation.
Activated silica, polyelectrolytes are other coagulation aids.

In low-temperature coagulation by metallic salts are adversely affected. T' effect is more pronounced when Alum used as a coagulant.
So here all the statements are correct.