Answer: Calcium.
- A Nitrogen
- B Potassium
- C Calcium
- D Magnesium
Correct answer: C. Calcium
Explanation: Blossom end rot of tomatoes is caused by calcium deficiency in the developing fruit. Calcium is poorly mobile in plants; irregular watering disrupts Ca transport. Affected tissue becomes dark, leathery, and sunken at the flower end.
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.