Wöhler's synthesis rearrangement identifies cyanate ion formula

Steps:

• Urea formula is CON₂H₄; ammonium provides NH₄, so cyanate ion supplies CON.
• Product notation (NH₄)NCO indicates atomic rearrangement from reactant NH₄OCN.
• Reactant ammonium cyanate thus contains OCN attached to NH₄⁺.
• Ion formula OCN⁻ matches structure ⁻O–C≡N and reaction with no byproducts.

Why C is correct:

• OCN⁻ is the standard cyanate ion formula, enabling isomerization NH₄OCN → (NH₂)₂CO per conservation of atoms.

Why the others are wrong:

• A: CON₂⁻ adds extra N, yielding CON₃H₄ incompatible with urea.
• B: CON⁻ uses incorrect atom order; cyanate bonds as O-C-N.
• D: NCO⁻ represents isocyanate ion, not cyanate.

Final answer: C