Answer: Trace elements.
- A Major elements
- B Trace elements
- C Bulk elements
- D Reserve elements
Correct answer: B. Trace elements
Explanation: Micronutrients (e.g. Fe, Mn, Zn, Cu, B, Mo, Cl) are needed in tiny amounts and are called trace elements.
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.