What are NPK fertilisers and what compounds do they contain?

NPK fertilisers are fertilisers that contain compounds of nitrogen, phosphorus, and potassium. These nutrients are essential for plant growth and improve agricultural productivity.

A strong answer should directly address the approved learning objective to define NPK fertilisers as fertilisers containing compounds of nitrogen, phosphorus and potassium. (Chemistry only). This question belongs to Production and uses of NPK fertilisers within The Haber process and the use of NPK fertilisers, so the response should use that exact curriculum context rather than a generic statement. The answer is correct when it names the key idea, explains the link to phosphorus, and keeps the wording specific to AQA GCSE revision.