Question

Which one is not a free living nitrogen fixer?

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

Answer 1

The correct option is C Rhizobium

The organisms involved in nitrogen fixation are termed 'nitrogen-fixing organisms'. They convert free nitrogen (gaseous form dinitrogen, $N_2$) into forms such as nitrates and nitrites that can be utilized by plants. These organisms could either be free-living or found in symbiotic, mutualistic, or commensalistic relationships with other plants.

Rhizobium is found in a symbiotic relationship with leguminous plant roots.

So, the correct answer is option C.