Correct Answer - B
Oscillatoria is a photosynthetic cyanobacterium. In this cyanobacteria during photosynthesis water is electron donor and oxygen is a byproduct, i.e., oxygenic photosynthesis occurs. Rhodospirillum and chlorobium are non-oxygenic photosynthetic, purple non-sulphur and green-sulphur bacteria. Chromatium is purple sulphur bacterium, also a non-oxygenic photosynthetic.
