Atoms that have filled outermost energy levels and do not participate in chemical bonding are called ions cations inert covalent

Inert.

Explanation:

The atoms that have filled the outermost shell with 8 atoms do not participate in any chemical reaction or they do not even bond with other atoms to form bond.

These atoms are known as inert atoms. They do not participate in any bond formation or chemical reaction because they are stable. They have 8 or 18 atoms in the outermost shell which makes them stable.

Example: Argon, krypton et cetera.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."