Which one of the following is the principle 'Nitrogen' fixing algal community of blue-green algae?

Answer: Option B

Anabena is one of the principle "Nitrogen fixing" algal communities of blue-green algae.
Anabena is found as plankton in shallow water and on moist soil with beadlike or barrel like cells and interspersed enlarged spores to provide nitrogen to plants in soluble forms.