The correct option is C reductive amination
Glutamate dehydrogenase enzyme helps in the process of reductive amination. During reductive amination, ammonia reacts with α-ketoglutaric acid and forms glutamic acid. The glutamic acid helps in the synthesis of other amino acids by the process of transamination.
Nitrogenase enzyme helps in the process of nitrogen fixation.
Ammonia monooxygenase enzyme plays a key role in nitrification in certain bacteria. It is involved in initial steps in nitrification where ammonia is oxidised and subsequently converted to nitrate.