Statements on nitrogen fertiliser processes:\nWhich of the following is correct regarding urea/AN manufacture and by-products?

Introduction / Context:
Industrial nitrogen fertilisers include ammonium nitrate (AN) and urea. Safety, equilibrium, and quality aspects are central to plant design and agronomy. This question checks knowledge of reaction energetics, synthesis stoichiometry, and the agronomic impact of impurities such as biuret formed by urea condensation at high temperatures.

Given Data / Assumptions:

• AN forms from ammonia and nitric acid in a neutralization reactor.
• Urea forms from ammonia and carbon dioxide via ammonium carbamate.
• Biuret forms when urea condenses at elevated temperature during finishing.

Concept / Approach:
The AN neutralization is strongly exothermic, providing heat for concentration. In urea synthesis, increasing the NH3/CO2 ratio generally aids conversion to urea (ammonia excess), not decreases it. Biuret is phytotoxic above certain levels; fertiliser-grade urea is specified with low biuret content to avoid seedling damage and animal health issues when misused.

Step-by-Step Solution:

Verification / Alternative check:
Plant design texts list AN neutralizer heat duties as net exothermic; urea synthesis models show improved conversion with ammonia excess; agronomy guides caution against high-biuret urea for sensitive crops.

Why Other Options Are Wrong:

• (a) Endothermic claim contradicts neutralization thermochemistry.
• (b) Decrease in yield with higher NH3/CO2 contradicts equilibrium trends.
• (d) Includes (b), which is false.
• (e) Includes multiple false assertions.

Common Pitfalls:
Assuming all neutralizations are mild; AN is notably exothermic. Confusing optimal NH3/CO2 with infinite excess—excess helps conversion but is balanced against corrosion and stripping duties.

Final Answer:
Biuret, an intermediate/by-product during urea manufacture, is toxic to seeds and animals