Urea synthesis stoichiometry:\nIndustrial urea (a nitrogenous fertilizer) is produced by reacting carbon dioxide with ________.

Introduction / Context:
Urea, labeled 46-0-0 in fertilizer analysis (N-P2O5-K2O), is produced in massive volumes for agriculture. Its synthesis couples the upstream ammonia plant with carbon dioxide recovered from reforming/shift units, thereby integrating carbon management with nitrogen fixation in a single complex.

Given Data / Assumptions:

• Inputs available on-site: ammonia (from Haber–Bosch) and carbon dioxide (from reforming and CO2 removal).
• Process steps: carbamate formation followed by dehydration to urea.
• We identify the direct chemical counterpart to CO2 in urea production.

Concept / Approach:
In the high-pressure synthesis section, ammonia reacts with carbon dioxide to form ammonium carbamate (NH2COONH4). Under elevated temperature and pressure, this intermediate dehydrates to urea (CO(NH2)2) and water. Unconverted carbamate is recycled after decomposition and recovery. Thus, the immediate reactant pairing for CO2 is ammonia, not nitric acid or other nitrogen oxides.

Step-by-Step Solution:
CO2 + 2 NH3 → NH2COONH4 (ammonium carbamate).NH2COONH4 → CO(NH2)2 + H2O (dehydration to urea).Recycle unconverted species and recover product via prilling or granulation.

Verification / Alternative check:
All commercial urea technologies (e.g., Stamicarbon, Saipem/Snamprogetti) implement the same chemical sequence of carbamate formation and dehydration using NH3 and CO2 as reactants.

Why Other Options Are Wrong:
Nitric acid and nitric oxide are used in nitric acid manufacturing and downstream nitrate fertilizers; ammonium nitrate is itself a fertilizer product formed from NH3 and HNO3, not a urea precursor; hydrogen is a reactant for ammonia synthesis, not urea formation.

Common Pitfalls:
Confusing “ammonia to nitrates” with “ammonia to urea”; they are separate product lines in a nitrogen complex.

Final Answer:
ammonia