The essentiality of Molybdenum was discovered by

Correct option is B

The correct answer is (B) D. I. Arnon and P. R. Stout

Explanation:
• Molybdenum (Mo) is a micronutrient essential for plant growth, particularly for nitrogen metabolism.
• Its essentiality was established by Daniel I. Arnon and Perry R. Stout in 1939 while working at the University of California, Berkeley.
• They demonstrated that plants could not complete their life cycle without minute amounts of Mo, satisfying the 'Criteria of Essentiality' which they themselves largely defined.
• Mo is a key component of enzymes like nitrogenase (for nitrogen fixation in legumes) and nitrate reductase (for converting nitrate to ammonia).
• Without Mo, plants exhibit symptoms like 'whiptail' in cauliflower or general nitrogen deficiency symptoms.

Information Booster:
• Arnon and Stout's three criteria for element essentiality are: 1. The plant cannot complete its life cycle without it. 2. The function is specific and cannot be replaced by another element. 3. The element is directly involved in metabolism.
• Molybdenum is unique because it is the only micronutrient whose availability increases with an increase in soil pH.

Additional Knowledge:
• A. L. Sommer and C. P. Lipman (Option A): Known for discovering the essentiality of Copper (Cu) and Zinc (Zn) in 1931.
• C. Sprengel (Option C): Famous for the 'Law of the Minimum' (1828), later popularized by Justus von Liebig.
• G. Gries and P. H. Brown (Option D): Associated with the discovery of Nickel (Ni) essentiality in the late 1980s.