The correct option is
B Mo
Macroelements are nutrients that are required in larger amounts by plants and other living organisms. Carbon(C), hydrogen (H), nitrogen (N), oxygen (O), phosphorous (P), potassium (K), calcium (Ca), sulfur (S), and magnesium (Mg) are macroelements.
Microelements are nutrients that are required in smaller amounts. Boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni). and cobalt (Co) are microelements.
Thus, the correct answer is option (D).