iGCSE Chemistry (0620) Core:10.2 Fertilisers: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
NPK fertilisers contain the elements nitrogen (N), phosphorus (P), and potassium (K) to promote healthy plant growth. Looking at the options, sodium nitrate ($\text{NaNO}_3$) contains nitrogen, which is one of the three essential elements in NPK fertilisers. Nitrates and ammonium salts are commonly used as sources of nitrogen in fertilisers. Aluminium sulfate, magnesium chloride, and calcium ethanoate do not contain nitrogen, phosphorus, or potassium in forms suitable for fertilisers. Therefore, sodium nitrate is the only salt that could be used as a component of an NPK fertiliser, making option A correct.
▶️ Answer/Explanation
Detailed solution:
Plants need three primary elements: nitrogen (N), phosphorus (P), and potassium (K). We need two compounds that between them contain all three. Potassium nitrate (KNO₃) provides nitrogen and potassium. Calcium phosphate (Ca₃(PO₄)₂) provides phosphorus. Together, they supply all three essential elements: N, P, and K. The other combinations either miss one element or do not provide all three between the two compounds.
▶️ Answer/Explanation
Detailed solution:
Fertilisers are labelled as NPK, which stands for the three essential elements they supply: Nitrogen (N), Phosphorus (P), and Potassium (K). Plants need these in relatively large amounts, and they are often depleted from soil by crops. So, the elements replaced are N, P, and K.