Question

Denitrification is the process of conversion of:
A. Ammonia into nitrates
B. Nitrate salts to free nitrogen
C. Complex organic compounds into ammonia.
D. Free nitrogen to ammonia.

Answer 1

Nitrification is the conversion of ammonia into nitrite followed by nitrite to nitrate. The whole process is a biological two step oxidation. Denitrification is the reverse of nitrification in which the nitrate undergo transformation.

Complete step by step answer:
Denitrification is the process of conversion of nitrate to nitrogen gas, through a series of intermediate gaseous nitrogen oxides. Specifically this is a microbial assisted process which reduces the nitrate present in the atmosphere to dinitrogen. Dinitrogen gas (${N_2}$ ) is the final product of denitrification, but several other intermediate gaseous are formed and some of them are hazardous to the environment.
The step by step denitrification process is shown as
$N{O_3}^ - \to N{O_2}^ - \to NO \to {N_2}O \to {N_2}$
The corresponding balanced redox reaction is shown as
$2N{O_3}^ - + 10{e^ - } + 12{H^ + } \to {N_2} + 6{H_2}O$
In the gaseous nitrogen oxides gases like nitrous oxide (${N_2}O$ ) are produced which is a greenhouse gas. This gas leads to ozone depletion and results in global warming thereby contributing to air pollution.
Not at all like nitrification, denitrification and anaerobic handling, happening for the most part in soils and dregs and anoxic zones in lakes and seas. Comparative to nitrogen obsession, denitrification is carried out by an assorted bunch of prokaryotes, and there's later proved that a few eukaryotes are too able of denitrification (Risgaard-Petersen et al.$2006$). A few denitrifying bacteria are the genera Bacillus, Paracoccus, and Pseudomonas. Denitrifiers are chemoorganotrophs and hence must moreover be provided with a few frames of natural carbon.
Denitrification is imperative in that it evacuates settled nitrogen (i.e., nitrate) from the biological system and returns it to the air in an organically idle frame (${N_2}$ ). This is often especially vital in farming where the misfortune of nitrates in fertilizer is inconvenient and costly. However, denitrification in wastewater treatment plays a really useful part by evacuating undesirable nitrates from the wastewater gushing, in this manner lessening the chances that the water released from the treatment plants will cause undesirable results (e.g., algal blooms).

Note:
Denitrification is commonly utilized to expel nitrogen from sewage and metropolitan wastewater. It is additionally an instrumental handle in built wetlands and riparian zones for the anticipation of groundwater contamination with nitrate coming about from over the top agrarian or private fertilizer utilization.