A free living nitrogen fixing cyanobacterium, which can also form symbiotic association with the water fern Azolla is

Options

(a) Tolypothrix
(b) Chlorella
(c) Nostoc
(d) Anabaena

Correct Answer:

Anabaena

Explanation:

Anabaena is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern.