Question

Mention the correct sequence of the formation of compounds during biological nitrogen fixation.
A. Hydrazine
B. Nitrogen
C. Ammonia
D. Diamide
Choose the correct answer from the options given below:

• A. A, D, C, B
• B. C, D, A, B
• C. D, A, B, C
• D. B, D, A, C

Hint:

Remember the reduction sequence: Nitrogen (Triple bond) $\rightarrow$ Diamide (Double) $\rightarrow$ Hydrazine (Single) $\rightarrow$ Ammonia (Finished).

Answer 1

The Correct Option is D

Concept: Biological nitrogen fixation by the nitrogenase enzyme is a stepwise reduction process where two atoms of nitrogen are gradually saturated with hydrogen.

Step 1: The Starting Point.
The process begins with atmospheric Nitrogen ($N \equiv N$) (B) binding to the enzyme complex.

Step 2: Stepwise Reduction.
The triple bond is broken in three stages of two-electron additions:
• Stage 1: Addition of 2H creates Diamide ($HN = NH$) (D).
• Stage 2: Addition of another 2H creates Hydrazine ($H_2N - NH_2$) (A).

Step 3: The Final Product.
The final addition of 2H (total 6 electrons) breaks the remaining single bond to produce two molecules of Ammonia ($NH_3$) (C).