Q. Which among the following is NOT a primary nutrient for plants? 
Answer: Magnesium
Notes: Apart from air, 15 of the essential nutrients are supplied by the soil to plants. Out of them, Nitrogen, Phosphorus and Potassium are called primary nutrients or macronutrients. Three more elements viz. Calcium, Magnesium and Sulphur are known as secondary nutrients because the deficiency of them is less likely to be a growth limiting factor. 

This question is part of 40000+ General Studies MCQ Series Course on GKToday Android app. Question Number: 14 in 14. Photosynthesis, Respiration and Nutrition in Plants in above course in App.