Which nitrogen cycle process is occurring when nitrogen in plant or animal protein is converted to ammonium?

Which of these nitrogen molecules would be present in the atmosphere?

Which of these nitrogen cycle processes converts atmospheric nitrogen to a soil form of nitrogen that is usable by plants?

Which of these nitrogen cycle processes takes nitrogen from its largest reservoir?

When deciduous trees shed their leaves, specialized soil bacterial will consume the leaf material for energy and, in the process, will return some of the leaf nitrogen to the soil. What nitrogen cycle process is taking place?

According to this diagram, plants use nitrogen to make _________________________