Answer: magnesium.
- A magnesium
- B iron only
- C calcium only
- D sodium only
Correct answer: A. magnesium
Explanation: Each chlorophyll molecule has a magnesium ion at the centre of its ring.
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.