In fertilizer chemistry, what is the correct condensed structural formula for biuret (the dimerization product formed when urea is overheated)?

Introduction / Context:
Biuret is a well-known impurity that can form when urea-based fertilizers are overheated or held too long at elevated temperature during processes such as melting and prilling. Understanding the correct structure of biuret is important for fertilizer quality control because excessive biuret can be phytotoxic, especially to sensitive crops and foliar applications.

Given Data / Assumptions:

• The question asks for the correct condensed structural formula of biuret.
• Biuret forms by condensation (with loss of ammonia) from urea molecules.
• We use standard, text-friendly condensed formulas without special drawing tools.

Concept / Approach:
Urea has the formula NH2CONH2. When two urea units condense, one –NH2 group and one –CO–NH– portion react with release of NH3, yielding a molecule that contains two carbonyl groups linked through a single bridging –NH–: H2N–CO–NH–CO–NH2. In condensed form, this is written as NH2CONHCONH2. Recognizing the repeating –CO–NH– motif is the key to distinguishing biuret from urea and from carbamate-type salts.

Step-by-Step Solution:
Start with urea: NH2CONH2.Overheating promotes condensation of two urea molecules with elimination of NH3.The product contains two carbonyls connected by –NH–, giving H2N–CO–NH–CO–NH2.Write as a single condensed string: NH2CONHCONH2.

Verification / Alternative check:
The molecular formula corresponding to NH2CONHCONH2 is C2H5N3O2, which matches the well-established composition of biuret. Textbook discussions of “biuret in urea fertilizers” consistently depict this structure.

Why Other Options Are Wrong:
NH2CONH2 (option A) is urea, not biuret. NH3COONH3 and NH4COONH2 (options B and D) represent ammonium carbamate or related salt-like formulations, not the amide-bridged dicarbonyl. Option E is not the correct connectivity for biuret and misplaces the amide linkage.

Common Pitfalls:
Confusing ammonium carbamate (an intermediate in urea manufacture) with biuret, or assuming biuret is simply “double urea” without the bridging –NH–. Also, some learners forget that biuret forms by loss of ammonia from urea under heat.

Final Answer:
NH2CONHCONH2