Final answer:
Among the elements listed, nitrogen (c) is not a micronutrient but rather a macronutrient required in larger quantities by plants. Iron, zinc, and manganese are all micronutrients needed in smaller amounts.
Step-by-step explanation:
When examining the essential elements for plant growth, we distinguish between macronutrients and micronutrients. Macronutrients are required in larger amounts, whereas micronutrients are needed only in small quantities, even though they play significant roles in the growth and development of plants. The main micronutrients include elements such as iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), and molybdenum (Mo). In contrast, elements like nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) are considered macronutrients because they are required in larger quantities by plants.
Answering the student's question, among the options provided: iron (a), zinc (b), and manganese (d) are indeed micronutrients because they are required in relatively small amounts by plants. However, nitrogen (c) is not a micronutrient but a macronutrient, as it is essential for plant growth in much greater quantities.