Question

The conversion of nitrates to nitrogen gas by bacteria is called
A. Denitrification
B. Nitrification
C. Nitrogen fixation
D. Excretion

Answer 1

The nitrogen cycle is a biogeochemical cycle in which nitrogen is transformed into numerous chemical forms as it moves through the atmospheric, land, and sea ecosystems. Nitrogen conversion can take place through both biological and physical processes. Nitrate is reduced to nitrogen gas by soil microbes when oxygen is not present.

Complete answer:
Fixation, ammonification, nitrification, and denitrification are all important processes in the nitrogen cycle. Atmospheric nitrogen makes up the majority of the Earth's atmosphere (78%), making it the most important source of nitrogen. However, the availability of atmospheric nitrogen for biological utilisation is limited, resulting in a scarcity of usable nitrogen in many ecosystems.

Ecologists are particularly interested in the nitrogen cycle because nitrogen availability can influence the rate of essential ecosystem processes such as primary production and breakdown. The global nitrogen cycle has been drastically affected by human activities such as the combustion of fossil fuels, the use of artificial nitrogen fertilisers, and the release of nitrogen in wastewater.

Denitrifying bacteria have been found in over 50 genera and 125 species, and they are thought to make up 10-15% of the bacteria population in water, soil, and sediment. Several species of Pseudomonas , Alcaligenes , Bacillus , and others denitrify nitrogen.
Denitrification is a microbially aided nitrate reduction process that can lead to the production of molecular nitrogen via a sequence of nitrogen oxide compounds.

Hence, the correct answer is (A) Denitrification.

Note:
Nitrogen is an essential component of living species' bodies. All proteins and dna include nitrogen atoms.In a process called as fixation, nitrogen is transformed from atmospheric nitrogen ($N_2$) to useful forms such as $NO_2$. Bacteria, the majority of which are symbiotic with plants, fix the majority of nitrogen.