Nitrosomonas and Nitrobacter cause nitrification are an obligate

✅ Explanation:
Nitrosomonas and Nitrobacter are classic examples of autotrophic bacteria. They obtain their energy from the oxidation of inorganic compounds (ammonia and nitrite, respectively) during the nitrification process. They do not rely on organic matter for their carbon or energy source.

📌 Other Options Explanations:
-(b) Heterotrophic bacteria: These bacteria derive their energy and carbon from organic matter. They cannot perform nitrification as they lack the metabolic pathways to oxidize inorganic nitrogen compounds.
– (d) Saprophytes: Saprophytes are organisms that obtain their nutrients from decaying organic matter. While they play a crucial role in decomposition.