Which of the following is the primary way in which nitrogen is returned to the atmosphere?

Denitrification is the primary way in which nitrogen is returned to the atmosphere. It is a process in the nitrogen cycle where bacteria convert nitrates back into atmospheric nitrogen. This process occurs in environments with low levels of oxygen, such as soil and waterlogged areas. Denitrifying bacteria use nitrate (NO₃^-) as an electron acceptor and release nitrogen gas (N₂) back into the atmosphere.

The process of denitrification plays a crucial role in the nitrogen cycle, as it helps to recycle nitrogen back into the atmosphere. This process is important in maintaining the balance of nitrogen in the environment and is necessary for the growth of plants and other organisms. Additionally, denitrification can help to mitigate the negative effects of excess nitrogen in ecosystems, such as the eutrophication of waterways.