Consider the following kinds of organisms :

1. Copepods
2. Cyanobacteria
3. Diatoms
4. Foraminifera Which of the above are primary producers in the food chains of oceans?

Autotrophs or primary producers are organisms that obtain their energy from sunlight and materials from nonliving sources.

Copepods are small crustaceans found in nearly every freshwater and saltwater habitat. They are major secondary producers in the ocean, forming a crucial link between phytoplankton, microzooplankton, and higher trophic levels like fish. Thus, they are not primary producers. Hence, statement 1 is not correct.

Cyanobacteria, also called blue-green algae, are microscopic organisms found naturally in all types of water. They are important primary producers and form part of the phytoplankton. They can also form biofilms and mats. Hence, statement 2 is correct.

Diatoms are photosynthesizing algae with a siliceous skeleton (frustule), found in almost every aquatic environment, including fresh and marine waters. Diatoms are one of the major primary producers in the ocean, responsible annually for approximately 20% of photosynthetically fixed CO2 on Earth. Hence, statement 3 is correct.

Foraminifera are single-celled organisms and amoeboid protists that use streaming granular ectoplasm to catch food. Therefore, they are not primary producers. Hence, statement 4 is not correct.

Therefore, only statements 2 and 3 are correct.