Answer:
D. marks transformation of nitrogen (N₂) from the atmosphere to ammonium (NH₄ plus) by bacteria.
Step-by-step explanation:
The nitrogen cycle is a biogeochemical cycle which involves transformation of atmoshperic nitrogen into many chemical forms including nitrite (NO2), nitrates (NO3) and ammonium (NH4).
The process of nitrogen cycle starts with the process of nitrogen fixation. In this process several nitrogen fixation bacteria such as cyno bacteria converts the atmospheric nitrogen into ammonium (NH4) in the soil. The resultant ammonium (NH4) can be directly used by plants or transform into nitrites or nitrates through nitrification process.
Hence, the correct option is D.