Which of the following organisms reduces nitrates in the soil to gaseous nitrogen?

The organism that reduces nitrates in the soil to gaseous nitrogen is a denitrifying bacterium. Denitrifying bacteria are microorganisms that can use nitrates as a source of oxygen for respiration, converting them into nitrogen gas (N2) which is then released into the atmosphere. This process is called denitrification and it plays an important role in the nitrogen cycle by returning nitrogen gas to the atmosphere and reducing the amount of available nitrogen in the soil. The other options are not involved in the process of denitrification. Euglena and protozoans are single-celled eukaryotic organisms that are not capable of denitrification. Parasitic molds are fungi that feed on living organisms, and nitrifying bacteria are involved in the conversion of ammonia to nitrate during nitrification, which is the opposite of denitrification.