Chemical rearrangement in Wöhler synthesis

Steps:

• Ammonium cyanate formula is NH₄X, where X is the cyanate ion; heating yields urea, NH₂CONH₂.
• Urea contains 2N, 4H, C, O; NH₄ provides 1N and 4H, so X must supply 1N, C, O.
• Balancing atoms shows X as OCN⁻, enabling NH₄OCN → NH₂CONH₂ isomerization.
• No other ion fits without extra atoms or imbalance.

Why C is correct:

• Cyanate ion is defined as OCN⁻ in inorganic nomenclature, matching the exact atomic composition for urea formation.

Why the others are wrong:

• A: CN⁻ is cyanide ion, lacks oxygen needed for urea's carbonyl group.
• B: CON⁻ is not a standard ion and would imbalance nitrogen count.
• D: NCO⁻ is isocyanate ion, forming NH₄NCO, which does not rearrange to urea.

Final answer: C