Which one of the following nutrients is not available in fertilizers ?

Fertilizers are commercially produced chemical substances used to provide essential nutrients to plants for better growth and yield. They are primarily categorized based on the primary macronutrients they supply, which are Nitrogen (N), Phosphorus (P), and Potassium (K). These three elements are required by plants in large quantities and are the core components of most standard commercial fertilizers (often labeled as NPK fertilizers).

• Nitrogen (B): Essential for vegetative growth and chlorophyll.
• Phosphorus (C): Vital for root development and energy transfer.
• Potassium (D): Important for overall plant health and water regulation.

Iron (A) is classified as a micronutrient. While it is essential for plant functions like chlorophyll synthesis, it is required in very small (trace) amounts. Most soils naturally contain sufficient iron, and it is generally not included in standard NPK fertilizers, making it the correct answer in this context.