Which two elements are commonly found in NPK fertilisers?

NPK fertilizers are specifically formulated to provide essential nutrients for plant growth, and they consist mainly of three key elements: nitrogen (N), phosphorus (P), and potassium (K).

In the context of the question, the pairing of potassium and phosphorus reflects two of the three primary macronutrients present in NPK fertilizers. Potassium is vital for regulating various physiological processes in plants, such as water regulation and enzyme activation, while phosphorus plays a crucial role in energy transfer and photosynthesis.

The other elements mentioned in the choices serve different roles and are not primary components of NPK fertilizers. Calcium and magnesium are important for plant growth and development but are not the defining elements in NPK. Sodium and chlorine are present in some contexts but are not part of the main nutrient trio associated with NPK fertilizers. Iron and copper are micronutrients required in smaller amounts but do not characterize NPK fertilizers. Thus, potassium and phosphorus stand out as the correct components reflecting the primary focus of NPK fertilizers.