747. Boron, Zinc and Manganese are usually referred to as

✅ The correct answer is option A.
Zinc, Chlorine, Boron, Molybdenum, Copper, Iron, Manganese, Cobalt and Nickel are called micro-nutrients. They are called so because they are found and needed by plants in very small amount relative to other nutrients and are least likely to be limiting plant growth and healthy development.