Calculate nitrogen mass percentage in urea (CO(NH₂)₂)

Steps:

• Urea's formula is CO(NH₂)₂, or CH₄N₂O, with molar mass 12 (C) + 4(1) (H) + 2(14) (N) + 16 (O) = 60 g/mol.
• Mass of nitrogen atoms: 2 × 14 = 28 g/mol.
• Percentage by mass: (28 / 60) × 100 = 46.7%.
• This matches option D.

Why D is correct:

• It equals (total N mass / molar mass) × 100, the standard formula for element percentage in a compound.

Why the others are wrong:

• A: Underestimates by using incorrect N atomic mass or formula.
• B: Assumes 25% N, possibly confusing with another fertilizer like ammonium nitrate.
• C: Calculates for single N atom (14/32, but urea has two N and molar mass 60).

Final answer: D