Question

Given below are two statements:
Statement (I): Molybdenum is a component of nitrate reductase, nitrogenase, xanthine oxidase/dehydrogenase and sulphite oxidase.
Statement (II): The critical concentration of molybdenum-deficiency in plants is usually more than 0.1 ppm and its deficiencies resemble the N-deficiencies.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Recall the standard list of Mo enzymes and the typical critical tissue level for Mo deficiency.

Answer 1

The Correct Option is C

The question tests two things about molybdenum, the enzymes it is built into, and the tissue level at which its deficiency shows up.

1. Both Statement (I) and Statement (II) are correct: Statement (I) checks out, but Statement (II) gets the direction of the critical concentration wrong, so this option fails.
2. Both Statement (I) and Statement (II) are incorrect: Statement (I) is a standard, correct list of Mo enzymes, so it cannot be called incorrect.
3. Statement (I) is correct but Statement (II) is incorrect: Nitrate reductase, nitrogenase, xanthine oxidase/dehydrogenase and sulphite oxidase are all genuine Mo-dependent enzymes, so (I) holds. For (II), the tissue level at which Mo deficiency appears is usually quoted around or below 0.1 ppm, not above it, so the "more than 0.1 ppm" claim runs the wrong way, making (II) incorrect overall even though the resemblance to N-deficiency is true.
4. Statement (I) is incorrect but Statement (II) is correct: Statement (I) is factually accurate, so this option is wrong too.

Molybdenum is needed in the smallest quantity of any plant micronutrient, and its deficiency threshold sits at or below 0.1 ppm dry matter, not above it. Because plants use Mo in enzymes tied to nitrogen metabolism, nitrate reductase and nitrogenase, a shortage of Mo blocks nitrogen use inside the plant, which is exactly why Mo deficiency looks so much like plain nitrogen starvation.

Let's summarize:

• Mo is a genuine cofactor for nitrate reductase, nitrogenase, xanthine oxidase/dehydrogenase and sulphite oxidase, so Statement (I) is correct.
• The critical Mo concentration is usually around or below 0.1 ppm, so calling it "more than 0.1 ppm" makes Statement (II) incorrect, despite its correct point about N-deficiency-like symptoms.

So the right choice is option 3, Statement (I) correct and Statement (II) incorrect.