The correct answer is A. ammonia.
Ammonia is the most important nitrogenous fertilizer. It is produced by the Haber-Bosch process, which combines nitrogen and hydrogen gas at high pressure and temperature. Ammonia is then used to make other nitrogenous fertilizers, such as ammonium nitrate and ammonium sulfate.
Nitric acid is a strong acid that is used to make other chemicals, such as explosives and dyes. It is not a major source of nitrogenous fertilizers.
Nitrogen is a gas that is found in the air. It is not a major source of nitrogenous fertilizers because it is difficult to extract from the air.
Nitrogen dioxide is a gas that is produced by burning fossil fuels. It is a pollutant that can cause acid rain and smog. It is not a major source of nitrogenous fertilizers.
In conclusion, the chief source for the production of nitrogenous fertilizers is ammonia.