Mass percentage of nitrogen via molar mass calculations

Steps:

• Molar mass of NH₄NO₃: N (2×14=28) + H (4×1=4) + O (3×16=48) = 80 g/mol.
• %N in NH₄NO₃: (28/80) × 100 = 35%.
• Molar mass of Ca(NO₃)₂: Ca (40) + N (2×14=28) + O (6×16=96) = 164 g/mol.
• %N in Ca(NO₃)₂: (28/164) × 100 ≈ 17%.

Why D is correct:

• Mass percentage formula (% = (mass of element / molar mass of compound) × 100) gives exactly 35% N in NH₄NO₃ and 17% N in Ca(NO₃)₂.

Why the others are wrong:

• A: Reverses the percentages between compounds.
• B: Correct for first but underestimates second (ignores full molar mass).
• C: Overestimates first and severely underestimates second.

Final answer: D