Counting N, P, K presence in fertilizer compounds Steps:

• Ammonium phosphate ((NH₄)₂HPO₄) contains N (from NH₄) and P (from PO₄), no K → 2 elements.
• Ammonium nitrate (NH₄NO₃) contains N (from NH₄ and NO₃), no P or K → 1 element.
• Potassium nitrate (KNO₃) contains K and N (from NO₃), no P → 2 elements.
• Sodium phosphate (Na₃PO₄) contains P (from PO₄), no N or K → 1 element. Why B is correct:
• B (2 1 2 1) exactly matches the element counts from the chemical formulas of the four compounds. Why the others are wrong:
• A (1 1 1 2): Undercounts first and third compounds, which each have two elements.
• C (1 2 1 1): Overcounts second compound, which has only N.
• D (2 2 2 1): Overcounts second compound as having two elements instead of one. Final answer: B