One modern idea on the origin of life states that simple organic molecules such as water vapor, carbon dioxide, nitrogen, methane, and ammonia were mixed together to create life. what was the mixture called?

Sounds quite appealing as the molecules listed are relatively common. However, they are only reactive under precise environmental conditions, including energy, which are far from adequate to produce the progressively higher levels of complexity required for the levels of biochemical assembly needed for life.

The next higher levels also require sulfur and phosphorus for the formation of homochiral amino acids and sugars, which are elemental level molecules required for DNA construction, which is found in all living things. These ostensibly are the "organic molecules" but only function as homochiral versions.

The mixture is solids, liquids and gases, which makes a name of mythical primordial or prebiotic soup most likely.

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