Which one of the following is not correctly matched?

Correct answer: (d) Azolla - Maize

Explanation

Blue-green algae (Cyanobacteria) fix nitrogen in paddy fields, and Rhizobium leguminosarum nodulates pea.

Azotobacter is a free-living nitrogen fixer associated with wheat.

Azolla is a water fern (with Anabaena) used as a biofertiliser in paddy/rice, not maize, so this pair is wrong.