Which of the following is a nitrogen fixer?

Choose the incorrect pair$(s)$:
$(I)$ Free-living nitrogen-fixing aerobic microbes - Beijerinckia
$(II)$ Rhodospirillum - Aerobic microbes
$(III)$ Bacillus - Free-living
$(IV)$ Cyanobacteria - Anabaena and Azotobacter

What is the function of Molybdenum?

Which of the following is a free-living,aerobic,and non-photosynthetic nitrogen-fixing bacterium?

Which one of the following produces nitrogen-fixing nodules on the roots of $Alnus$?

Identify the non-leguminous plants that form nodules to fix nitrogen.