The correct option is 2 (Cyanobacteria) and 3 (Diatoms) as primary producers in oceanic food chains because both play critical roles in photosynthesis, converting sunlight into energy and producing organic matter. Cyanobacteria are significant contributors to oceanic primary productivity, especially in nutrient-poor waters, while diatoms, being a group of microalgae, are key components of phytoplankton that form the base of marine food webs. Their ability to utilize sunlight and inorganic nutrients establishes them as foundational organisms that support marine ecosystems, as discussed in standard resources like NCERT and other ecological studies.