International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What type of substances typically comprise NPK fertilisers?

1. Organic acids

2. Inorganic salts

3. Heavy metals

4. Alkaloids

The correct answer is: Inorganic salts

NPK fertilizers are primarily composed of inorganic salts, which are essential for providing the three key nutrients: nitrogen (N), phosphorus (P), and potassium (K). These nutrients play a critical role in plant growth, promoting processes such as photosynthesis, energy transfer, and nutrient transport. Inorganic salts are typically very soluble in water, which allows for easy absorption by plants through their roots. They can come from various chemical compounds, such as ammonium nitrate for nitrogen, superphosphate for phosphorus, and potassium chloride for potassium. The uniformity and predictable nature of inorganic salts also make them highly effective in supplying nutrients in a controlled manner. Other types of substances mentioned, such as organic acids, heavy metals, and alkaloids, do not typically form the basis of NPK fertilizers. Organic acids may have some relevance in soil chemistry but do not serve as the primary nutrient source in fertilizers. Heavy metals are generally undesirable in fertilizers due to their toxic nature and potential to contaminate soil and water. Alkaloids are organic compounds that typically have biological activity and are not associated with plant nutrition in the context of fertilizers.