__________ is the undesirable by-product produced in the manufacture of urea.

ANS:B - Biuret

Biuret is a compound that forms as an undesirable by-product during the manufacture of urea, a nitrogenous fertilizer. Biuret is chemically represented as NH2CONHCONH2. It is produced when urea molecules undergo a condensation reaction under certain conditions, typically at elevated temperatures during urea synthesis processes. Here's an explanation of biuret and its significance:

1. Formation: Biuret forms when two urea molecules (NH2CONH2) react with each other, releasing a water molecule (H2O) in the process. The chemical reaction can be represented as follows: 2𝑁𝐻2𝐶𝑂𝑁𝐻2→𝑁𝐻2𝐶𝑂𝑁𝐻𝐶𝑂𝑁𝐻2+𝐻2𝑂2NH2​CONH2​→NH2​CONHCONH2​+H2​O This reaction occurs when urea is subjected to high temperatures, such as during urea synthesis or processing.
2. Structure: Biuret is a cyclic compound containing two urea groups linked by a carbonyl (-CO-) group. It has a relatively simple structure compared to urea and is often considered an impurity or by-product in urea production processes.
3. Undesirable Properties: Biuret is considered undesirable in urea-based fertilizers for several reasons:
   • Toxicity: Biuret can be toxic to plants, particularly when present in high concentrations. It can inhibit plant growth, cause leaf burn, and reduce crop yields.
   • Regulatory Compliance: Many agricultural standards and regulations specify limits for biuret content in urea fertilizers to ensure product quality and minimize potential harm to crops.
   • Product Performance: High biuret content in urea fertilizers can affect product performance and efficacy, leading to uneven nutrient distribution, reduced nutrient uptake by plants, and potential environmental contamination.
4. Control and Mitigation: Urea manufacturers employ various strategies to control and minimize biuret formation during urea production. These may include optimizing reaction conditions, adjusting process parameters, and employing purification techniques to remove biuret from the final product.

Overall, while biuret forms as a by-product during urea manufacture, its presence needs to be minimized to ensure the quality, safety, and effectiveness of urea-based fertilizers. Regulatory standards and industry practices aim to control biuret levels to meet agricultural requirements and ensure optimal performance in crop production.