Which three main elements are commonly used in fertilizers?

The correct answer highlights the three primary macronutrients that are essential for plant growth and are commonly included in fertilizers: nitrogen, phosphorus, and potassium. These elements are known as NPK, which is an acronym frequently used in agriculture to denote their importance.

Nitrogen is crucial for vegetative growth, as it is a key component of amino acids and proteins, and it plays a role in chlorophyll production, which enables photosynthesis. Phosphorus contributes to root development, flowering, and fruiting, being key in energy transfer and storage via ATP (adenosine triphosphate). Potassium enhances overall plant health, improving water regulation, disease resistance, and the synthesis of proteins and starches.

In contrast, while carbon, hydrogen, and oxygen are vital for plants—they are integral components of carbohydrates and water—these elements are typically derived from the air and the soil rather than being directly added through fertilizers. The other options include elements that are important in smaller amounts or specific functions in plant metabolism but do not serve as the primary nutrients primarily emphasized for agricultural fertility. Thus, nitrogen, phosphorus, and potassium are indispensable for comprehensive fertilizer formulations that promote optimal plant growth.