Calculate % nitrogen by mass for each fertilizer

Steps:

• Percentage nitrogen = (total atomic mass of N atoms / formula mass) × 100.
• For A (NH₄NO₃): 2 N atoms × 14 = 28; 28/80 × 100 = 35%.
• For B ((NH₄)₃PO₄): 3 N × 14 = 42; 42/149 × 100 ≈ 28%.
• For C ((NH₄)₂SO₄): 2 N × 14 = 28; 28/132 × 100 ≈ 21%.
• For D (KNO₃): 1 N × 14 = 14; 14/101 × 100 ≈ 14%.

Why A is correct:

• Ammonium nitrate has the highest %N (35%) because it contains two N atoms in a low formula mass, maximizing N proportion per mass unit.

Why the others are wrong:

• B has lower %N (28%) due to three N atoms diluted by heavier phosphate group.
• C has lower %N (21%) from sulphate's higher mass relative to two N atoms.
• D has lowest %N (14%) with only one N atom and added potassium mass.

Final answer: A