What is the difference between inorganic and organic compounds?

The main difference is in the presence of a carbon atom; organic compounds will contain a carbon atom (and often a hydrogen atom, to form hydrocarbons), while almost all inorganic compounds do not contain either of those two atoms. ... Meanwhile, inorganic compounds include the salts, metals, and other elemental compounds.

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