Which of the following is a source of potassium for NPK fertilisers?

The correct option is Potassium chloride. This answer is correct because it matches the approved learning objective to explain that industrial production of NPK fertilisers can use several raw materials and integrated processes. (Chemistry only) in the subtopic Production and uses of NPK fertilisers.

The correct option is Potassium chloride. Potassium chloride is correct because it directly supports the approved learning objective to explain that industrial production of NPK fertilisers can use several raw materials and integrated processes. (Chemistry only). This belongs to the subtopic Production and uses of NPK fertilisers within The Haber process and the use of NPK fertilisers, so the explanation must stay tied to that curriculum context. The other options are incorrect because they either do not answer this learning objective, use a vague statement, or move away from Production and uses of NPK fertilisers.