Answer: Nitrogen.
- A Manganese
- B Boron
- C Nitrogen
- D Zinc
Correct answer: C. Nitrogen
Explanation: Nitrogen is the macronutrient needed in the largest quantity by plants. It is a component of amino acids, proteins, nucleic acids, and chlorophyll. It is the most common limiting nutrient in agriculture.
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.