Through which process is inorganic nitrogen-containing ions converted into organic molecules? 

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

Assimilation is the process by which inorganic nitrogen-containing ions (such as ammonium and nitrate) are converted into organic molecules, such as amino acids, nucleotides, and chlorophyll. This process occurs in plants and other organisms that can use nitrogen to synthesize these organic compounds. Denitrification, nitrogen fixation, and nitrification are all processes that involve the conversion of nitrogen in various forms, but they do not involve the synthesis of organic molecules from inorganic nitrogen ions.