The correct option is
C Trace element
There are about 17 elements which are essential for the functioning of plants.
Major nutrients: Nitrogen (N), Phosphorus (P) and Potassium (K).
Secondary nutrients : Calcium (Ca), Magnesium (Mg) and Sulphur (S).
Micronutrients or trace elements: Boron (B), Chlorine (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo) and Zinc (Zn).
Macronutrients are required in large amounts by plants while micronutrients are required in small amounts in plants.
Thus, the correct answer is option A.