The correct option is C Zooplankton - Primary producer
in an aquatic food chain, primary producers are phytoplanktons. They are autotrophic microscopic organisms that inhabit the upper sunlit layer of almost all oceans and bodies of fresh water on Earth. They form the first trophic level. Zooplanktons feed on the phytoplanktons. They are primary consumers and belong to the second trophic level. Thus the correct answer is option C.