Question

Match LIST-I with LIST-II 

LIST-I		LIST-II
A.	Biological nitrogen fixation	I.	Nitrobacter
B.	Conversion of ammonia to nitrite	II.	Paracoccus
C.	Conversion of nitrite to nitrate	III.	Rhizobium
D.	Denitrification	IV.	Nitrosomonas

Choose the correct answer from the options given below: 
 

• A. A-II, B-III, C-IV, D-I
• B. A-III, B-IV, C-I, D-II
• C. A-I, B-III, C-II, D-IV
• D. A-I, B-II, C-III, D-IV

Hint:

For nitrification, remember the order and the names: {Nitro{so}monas} works on ammonia ({so}urce), which comes first. {Nitro{bacter}} works on the product of the first step (nitrite), coming second.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This question requires matching key processes of the nitrogen cycle (LIST-I) with the specific genus of bacteria responsible for carrying out that process (LIST-II).
Step 2: Detailed Explanation:
A. Biological nitrogen fixation: This is the conversion of atmospheric nitrogen (\(N_2\)) into ammonia (\(NH_3\)). III. {Rhizobium} is a classic example of a bacterium that performs this symbiotically in the root nodules of legumes. So, A matches III.
B. Conversion of ammonia to nitrite: This is the first step of nitrification. It is carried out by ammonia-oxidizing bacteria, a prime example of which is IV. {Nitrosomonas}. So, B matches IV.
C. Conversion of nitrite to nitrate: This is the second step of nitrification. It is carried out by nitrite-oxidizing bacteria, the most common example being I. {Nitrobacter}. So, C matches I.
D. Denitrification: This is the process of converting nitrate (\(NO_3^-\)) back to nitrogen gas (\(N_2\)). This is performed under anaerobic conditions by denitrifying bacteria such as II. {Paracoccus} (and also Pseudomonas). So, D matches II.
Step 3: Final Answer:
The correct set of matches is A-III, B-IV, C-I, D-II.