The correct option is B Zooplankton
Zooplankton
Zooplanktons are primary consumers which feed on the producers, i.e, phytoplanktons. These include microscopic animals, crustaceans, small insects, etc.
Zooplanktons form the second most important trophic level because they are ones that feed on plants and make the food prepared by the plants or producers available to the secondary and tertiary consumers.
Phytoplankton
Phytoplanktons are photosynthetic microscopic plants that occupy the first trophic level of producers. They can prepare their own food using sunlight and inorganic substances such as carbon dioxide and water.
This is primarily the most important trophic level as phytoplanktons in an aquatic ecosystem are the ultimate producers of food. They trap the energy of sunlight and convert it into chemical energy stored in food. All other living organisms directly or indirectly depend on them for food.
Benthos
Benthos is a community of organisms living on the sea bed. It does not represent a specific trophic level.
Neuston
Neuston is the community of organisms inhabiting the water surface of the water bodies. It does not represent a specific trophic level.
Final answer
(A) Zooplankton