The first stable product of fixation of atmospheric nitrogen in leguminous plants is
A. \[NO{{2}^{-}}\]
B. Ammonia
C. \[NO{{3}^{-}}\]
D. Glutamate

Hint: A variety of symbiotic relationships that fix nitrogen are found, but the most significant among them is the legume-bacteria relationship. Species such as Rhizobium, which is rod-shaped bacteria, have such associations as alfalfa, sweet clover, and sweet pea to the root of different legumes.

Complete answer: Nitrogen fixation, any natural or industrial method leading to the production of free nitrogen (N2), the air abundant relatively inert gas, interacts chemically with other elements in order to form more reactive nitrogen compounds such as ammonia, nitrates, and nitrites.
In nature, nitrogen is mixed with lightning or ultraviolet rays as nitric oxide, but the amount of nitrogen is more importantly fastened to soil microorganisms as ammonia, nitrites, and nitrates. They carry out more than 90% of all nitrogen fixation.
The first stability of atmospheric nitrogen fixation is ammonia. It needs \[16ATP\], a source of ferredoxin, \[NADPH\] or \[FMNH2\] hydrogen donor and dinitrogenase.
The nitrogen fixation bacterium has nitrogenase enzyme, which is found in the leguminous plant root nodules. A multi-step reaction catalyzed by the bacterial nitrogenase enzyme converts the free nitrogen gas to ammonium ions.
The nitrogen (N2) conversion process is referred to as the nitrogen fixation process.
\[N2\to N2H2\to N2H2\to 2NH3\]
(Nitrogen) (Diamide) (hydrazine) (Ammonia)
 \[2NH3+3O2\to 2NO2-+2H2O\]
\[2NO2+O2\to 2NO3-\]
Ammonia reacted by α-ketoglutaric acid and glutamic acid R forms in reductional animation
\[\alpha -ketoglutaric+NH4+NADPH\]
\[\xrightarrow[Dehydrogenase]{Glutamate}Glutamate+H20+NADPH\]
Nitrogen produces the stable substance, diamide (\[N2H2\]), hydrazine (\[N2H4\]), and ammonia.
Thus, choice (B), 'ammonia' is the correct answer.

Note: In the development of nitrogen-fixing nodules in roots of non-leguminous plants like Alnus, microbes like Frankia also support. The rhizobium and the Frankia live in the soil free of charge but are symbionts that can fix the nitrogen atmosphere. The aerobic microbes live like aerobics but become anaerobic at the time of nitrogen fixation.