Through which process is nitrate converted to nitrogen gas? 

A)  assimilation 
B)  denitrification 
C)  nitrification 
D)  nitrogen fixation

Denitrification is the process by which nitrate is converted to nitrogen gas. This process occurs through the reduction of nitrate to nitrite, then to nitric oxide, nitrous oxide, and finally to nitrogen gas. This process is carried out by denitrifying bacteria in oxygen-poor environments. Assimilation is the process by which plants and animals incorporate nitrogen into their tissues, nitrification is the process by which ammonia is converted to nitrate, and nitrogen fixation is the process by which atmospheric nitrogen is converted to a usable form by certain bacteria.