Q. Which one of the following is not an essential micronutrient for plants?
Answer: Sodium
Notes: There are 13 essential nutrients required by plants for its healthy and proper growth. Now these nutrients are divided into two categories:
Macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulphur)
Micronutrients (iron, copper, manganese, zinc, boron, molybdenum and chlorine)
Additional mineral nutrient elements which are beneficial but not necessary are sodium, cobalt, vanadium, nickel, solenium, aluminium and silicon. Thus boron, zinc and copper falls into category of essential micronutrients while sodium does not.  

This question is part of 40000+ General Studies MCQ Series Course on GKToday Android app. Question Number: 32 in 14. Photosynthesis, Respiration and Nutrition in Plants in above course in App.