The correct option is B non-symbiotic nitrogen-fixers
Azotobacter and Beijerinckia are examples of free-living nitrogen-fixing aerobic microbes. Since they are free-living, they are non-symbiotic in nature.
Rhizobium is an example of symbiotic nitrogen fixer.
Proteus and Pseudomonas are examples of ammonifying bacteria.
Mycobacterium is an example of a disease causing bacteria.