Urea, a commonly used nitrogen-based fertilizer, is prepared by the reaction between ammonia and ____.

Explanation

Industrial urea manufacture uses ammonia and carbon dioxide. The overall chemical equation is 2NH₃ + CO₂ → CO(NH₂)₂ + H₂O. The product CO(NH₂)₂ is urea, an important nitrogen fertiliser. Hydrogen and oxygen alone are not the missing carbon-containing reactant.