Which of the following convert the ammonia to nitrites?

Answer: Option D

Nitrosomonas and Nitrobacter can convert the ammonia to nitrites.
Nitrosomonas and Nitrobacter are chemoautotrophic organisms found in soil and water and are responsible for the oxidation of ammonium to nitrite (Nitrosomonas) and nitrite to nitrate (Nitrobacter).
Nitrification is the process that converts ammonia to nitrite and then to nitrate and is another important step in the global nitrogen cycle.