Nitrates are transformed into nitrogen by(a) Ammonifying bacteria (b) Nitrifying bacteria (c) Denitrifying bacteria (d) Both A and B

The correct answer is (c) Denitrifying bacteria.
The process of converting nitrates into nitrogen gas is known as denitrification, and it is carried out by denitrifying bacteria.
1. Denitrifying Bacteria:
o These bacteria convert nitrates (NO₃⁻) in the soil or water into nitrogen gas (N₂) or, in some cases, into nitrous oxide (N₂O), a process that is part of the nitrogen cycle.
o The conversion typically happens in anaerobic conditions (where oxygen is scarce), such as in waterlogged soils or deeper layers of the soil where oxygen does not readily reach.
o Denitrification helps return nitrogen to the atmosphere, completing the nitrogen cycle.
The general process of denitrification is as follows:
o Nitrate (NO₃⁻) → Nitrite (NO₂⁻) → Nitric oxide (NO) → Nitrous oxide (N₂O) → Nitrogen gas (N₂)
2. Other Bacteria:
o (a) Ammonifying bacteria: These bacteria break down organic matter (such as dead plants and animals) into ammonia (NH₃) or ammonium ions (NH₄⁺), not into nitrogen gas.
o (b) Nitrifying bacteria: These bacteria are involved in the process of nitrification, where ammonia is converted into nitrites (NO₂⁻) and then to nitrates (NO₃⁻), but not into nitrogen gas.
o (d) Both A and B: This option is incorrect because neither ammonifying nor nitrifying bacteria convert nitrates into nitrogen gas.
The transformation of nitrates into nitrogen gas is carried out by denitrifying bacteria in the nitrogen cycle. Therefore, the correct answer is (c) Denitrifying bacteria.