Question

A completely free living organism which takes part in nitrogen fixation is

• A. Anabaena
• B. Bacillus
• C. Azotobacter
• D. Rhizobium

Answer 1

The correct option is C Azotobacter

The atmospheric nitrogen is not available to plants. There are some nitrogen fixing bacteria which converts atmospheric nitrogen into ammonia which is readily available to plants. Azotobacter are free-living nitrogen fixing bacteria. Anabaena is a free-living nitrogen fixing bacteria. However, it also forms symbiotic association with plants like mosquito fern. Hence, they are symbiotic bacteria as well.
Thus, the correct answer is 'Azotobacter.'