Correct option is B
• Molybdenum is essential for nitrogen fixation (III) as it is a component of the nitrogenase enzyme.
• Manganese is involved in water oxidation (I) during the light reaction of photosynthesis.
• Magnesium is a central component of the chlorophyll molecule (II).
• Zinc plays a role in auxin synthesis (IV), a key plant hormone.
Thus, the correct matches are: A–III, B–I, C–II, D–IV.