Question

A nitrogen-fixing microbe associated with Azolla in rice fields is (a) Spirulina

Answer 1

The options aren't complete but the answer for this would be:

ANABAENA

Anabaena also referred to as Anabaena azollae.

Azolla is a free floating, fresh water fern (pteridophyte). Anabaena is a free living blue-green algae or cyanobacterium.

Sometimes, Anabaena is found in a symbiotic relationship with Azolla. Anabaena has nitrogenase enzyme present in it which helps in the process of Nitrogen Fixation.