Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Uptake of hydrogenase activity is a mechanism of removing hydrogen from the site of nitrogen activity which concurrently carries out reactions of nitrogen fixation and hydrogen production.
Reason (R): Acetylene reduction technique is a common method of measuring nitrogenase activity.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Hydrogenase = Recycling (Efficiency).
Acetylene Reduction = Measuring (Technique).
They are both about Nitrogenase, but one is about Survival and the other is about Science.

Answer 1

The Correct Option is B

Concept: This question evaluates knowledge of nitrogenase biochemistry and the laboratory techniques used to quantify its activity.

Step 1: Evaluating the Assertion.
Assertion (A) is correct. During nitrogen fixation, nitrogenase inevitably produces hydrogen ($H_2$) as a byproduct. Many efficient nitrogen-fixing bacteria possess an Uptake Hydrogenase (Hup) system. This enzyme recaptures the produced $H_2$ and recycles the electrons back into the system, increasing the overall energy efficiency of the process.

Step 2: Evaluating the Reason.
Reason (R) is also correct. The Acetylene Reduction Assay (ARA) is the standard method for measuring nitrogenase activity. Nitrogenase is "promiscuous" and will reduce acetylene ($C_2H_2$) into ethylene ($C_2H_4$). Since ethylene is easily measured via gas chromatography, it serves as a proxy for nitrogen-fixing activity.

Step 3: Determining the Relationship.
Both statements are accurate scientific facts. However, the fact that we can measure nitrogenase with acetylene (Reason R) does not explain *how* or *why* bacteria use hydrogenase to recycle hydrogen (Assertion A). Therefore, (R) is not the explanation for (A).