Which of the following is a free living aerobic non-photosynthetic nitrogen fixer ?
(a) Rhizobium
(b) Azotobacter
(c) Azospirillum
(d) Nostoc
Correct option**(b) Azotobacter**
Explanation :
Azotobacter is a free living, aerobic non-photosynthetic, i.e. saprophytic bacteria. It retains the capability of fixing atmospheric nitrogen, i.e. fixation of atmospheric dinitrogen into ammonia.
