Question

For conversion of atmospheric nitrogen to 4 ammonia, molecules how many ATP molecules are required?
A. 8
B. 16
C. 4
D. 32

Answer 1

Atmospheric nitrogen is present in the form of dinitrogen $(N_2)$. During nitrogen fixation, dinitrogen is converted into ammonia, which is a usable form. This process occurs as a series of reactions for which energy is required. This energy is in the form of ADP and ATP. In principle, one molecule of dinitrogen requires 16 ATP molecules to form 2 ammonia molecules.

Complete answer:
For the conversion of atmospheric nitrogen to 4 ammonia molecules, 32 molecules of ATP are required.
During nitrogen fixation, $N_2$ is converted into $NH_3$.
This process occurs as follows:
$N_2$ undergoes a reduction to form two molecules of $NH_3$.
During this reaction, 16 molecules of ATP are hydrolysed to form two molecules of ammonia.
So, to obtain 4 molecules of ammonia, we require 2 molecules of dinitrogen.
Therefore, the reduction of 2 molecules of $N_2$ would require 32 molecules of ATP to form 4 molecules of $NH_3$.

Hence, the correct answer is option (D).

Additional information:
Nitrogen fixation is a process by which atmospheric nitrogen is converted into a usable organic form. In the atmosphere, nitrogen is generally present in a molecular form $(N_2)$. This cannot be metabolised easily by the various plants and organisms. On the other hand, when it gets converted to $NH_3$, the plants and other organisms can easily use it and metabolise it.

Note: Nitrogen fixation can be carried out by some microorganisms that undergo photosynthesis to produce electrons during the reaction. 8 electrons are produced in the reaction. To transfer one electron, two molecules of ATP are required.
ATP also makes the reaction kinetically feasible. It does not make the reaction thermodynamically favourable.