Answer: Magnesium.
- A Iron
- B Zinc
- C Magnesium
- D Calcium
Correct answer: C. Magnesium
Explanation: Magnesium (Mg) is the central atom in the chlorophyll molecule. Deficiency of Mg causes interveinal chlorosis (yellowing between veins) especially in older leaves.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.