Which of the following is not a micronutrient?

Magnesium (Mg) is a macronutrient not a micronutrient. Such nutrients are required by plants in comparitively large amount ( $1-10 \mathrm{mg}$ per gram of dry matter). Other examples are Phosphorus (P), Potassium (K), Nitrogen (N), etc. Micronutrients are required by plant in traces, less than 0.1 mg per gram of dry matter. Boron (B), Zinc $(\mathrm{Zn})$ and Mangenese $(\mathrm{Mn})$ are micronutrients.