Which of the following is classified as a microelement essential for plant growth?

Iron is classified as a microelement essential for plant growth because it plays a crucial role in various physiological processes within plants. It is a vital component of chlorophyll, which is essential for photosynthesis, allowing plants to convert sunlight into energy. Additionally, iron is necessary for the functioning of certain enzymes that are involved in electron transport and nitrogen fixation.

In contrast, phosphorus, nitrogen, and calcium are classified as macronutrients. While they are also vital for plant growth, they are required in larger quantities compared to microelements. Phosphorus is important for energy transfer and the formation of DNA and RNA; nitrogen is essential for protein synthesis and overall plant development; and calcium aids in cell wall structure and stability. Thus, the classification of iron as a microelement highlights its specific role and the smaller quantities required by plants for optimal growth and development.