The use of sand and gravel filters to remove particulate matter from water is known as treatment. tertiary advanced secondary primary

Primary treatment is process of removing the floating materials and the remaining liquid then is discharged or subjected to secondary treatment.
Secondary treatment is the process of removing dissolved and suspended biological matter. This treatment is typically performed by indigenous, water-borne micro-organisms in a managed habitat.
Tertiary is the process used to refine and polish water before it is reused or discharged .
The use of sand and gravel filters to remove particulate matter from water is known as advanced treatment.
This treatment produce high quality water without the use of chemical aids.

No table found. the question asks for covalent bond based on electronegativies

The formula is (nh4)2co3