Question

Free-living nitrogen-fixing biofertilizer is
(a) Glomus
(b) Rhizobium
(c) Azotobacter
(d) Pseudomonas

Answer 1

Hint: It is a genus of diazotrophic free-living bacteria whose resting process is a cyst. It is present mostly in soils that are neutral to alkaline, in aquatic environments and on some plants. It has many metabolic capacities, including fixation of atmospheric nitrogen by ammonia conversion.

Complete answer:
Azotobacter is a genus of typically motile, oval or spherical bacteria that produce large amounts of capsular slime and form thick-walled cysts. They are aerobic, free-living soil microbes that play an important role in the nitrogen cycle in nature, binding inaccessible atmospheric nitrogen to plants and releasing it into the soil (nitrogen fixation) in the form of ammonium ions. It is used by humans for the processing of biofertilizers, food additives, and certain biopolymers, in addition to being a model organism for the study of diazotrophs. In 1901, the Dutch microbiologist and botanist, Martinus Beijerinck, discovered and identified the first representative of the genus, Azotobacter chroococcum. Gram-negative bacteria present in acidic and alkaline soils, in water, and in contact with certain plants are Azotobacter species.

Additional information:
Rhizobium is a genus of bacteria that is related to the formation of plant root nodules. These bacteria live together with legumes in symbiosis. They take atmospheric nitrogen and pass it on to the plant, allowing it to grow low in nitrogen in the soil. 
Slow-growing, typically benign tumours in the carotid arteries (major blood vessels in your neck) , the middle ear or the region below the middle ear (jugular bulb) are glomus tumours or paragangliomas. Glomus tumours are most often benign, but as they develop, they can cause serious damage to the surrounding tissues.
Pseudomonas is a common genus of bacteria that, under some conditions, can cause infections in the body. There are several forms of Pseudomonas bacteria that are distinct. An infection can only be caused by a few forms. In water, dirt, and damp areas, pseudomonas bacteria prefer to live and breed.
So, the correct answer is ‘(c) Azotobacter’.

Note: The cells show inclusions under magnification, some of which are coloured. The coloured inclusions were called "reproductive grains" or gonidia, a kind of embryo cell, in the early 1900s. The granules, however, were later determined not to participate in the division of the cells. The coloured grains consist of volutin, while drops of fat, which act as energy reserves, are the colourless inclusions.