Which abiotic factor differentiates between the three major types of aquatic biomes? (freshwater, estuary, marine) question 4 options: sunlight movement salinity oxygen

The correct answer is salinity.  

The aquatic biome can be differentiated into two fundamental regions, that is, marine, which includes estuaries and oceans, and freshwater that comprises rivers and ponds. The freshwater is illustrated as exhibiting a low salt concentration, that is, generally less than 1 percent. On the other hand, the marine regions comprise a higher quantity of salt concentration.  

it means there are 3 atoms of oxygen