An organism can make its own organic molecules using simple inorganic molecules. does it qualify as a heterotroph?

Heterotrophs are not able to produce their own food. Alternatively, they acquire from organic substances for energy and food. Heterotrophs cannot obtain organic substances from inorganic molecules. Therefore, no, an organism without the traits mentioned does not qualify to be classified as a heterotroph. 

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