Question

In the Nitrogen cycle, soil nitrates are transformed into free nitrogen by _________.
A. Nitrifying bacteria
B. Denitrifying bacteria
C. Ammonifying bacteria
D. Both 'a' and 'c'

Answer 1

Hint: It is very common to be known that the body of every organism on the planet consists of nitrogen. Also, the atmosphere is majorly filled with Nitrogen. Therefore, the amount of nitrogen needs to be circulated between the atmosphere and organisms to maintain balance.

Complete Answer
Nitrogen cycle is a process take place in five different steps that are described below:
Nitrogen fixation: It is the first step of this process that involves conversion of atmospheric Nitrogen into Ammonia by the action of bacterias like Azotobacter or Rhizobium. These bacterias are generally found in the leguminous roots of plants. This process can take place in case of lightning due to increased temperature.
Nitrification: This is the second step of the cycle that involves conversion of Ammonia into nitrates. Thus can be achieved in two steps, that is, first bacterias like Nitrococcus, Nitrosommonas act on the Ammonia to form Nitrates. Then these Nitrates are acted upon by another bacteria called Nitrobacter that converts it into nitrites.
Assimilation: This is the third step of the nitrogen cycle that is concerned with absorption of Nitrates, Nitrites into the soil. These components serve as nutritional sources to the plant body.
Ammonification: This is another step in the nitrogen cycle that is concerned with restoration of Ammonia from Nitrates or Nitrites molecules of plant or animal remains or their excretory products. This also involves a room of bacterias.
Denitrification: This is the last step of the Nitrogen cycle that involves reversal of reactions that took place in nitrification that is conversion of simple nitrogenous compounds back to Nitrogen.

Therefore, it is clear from these steps that in the Nitrogen cycle, soil nitrates are transformed into free nitrogen by denitrifying bacteria that is, option B. Therefore, it is the correct answer.

Note:
Nitrogen cycle can be defined as a biochemical process in which nitrogen (releasing out of dead remains of the body of organisms or their excretory products) keeps circulating between the atmosphere and Earth's surface by the action of microscopic bacterias.