Which of the following nitrogen containing compound does not give Lassaigne’s test ?

Explanation:-

• Phenylhydrazine (C₆H₅NHNH₂):
  • This compound contains an NHNH₂ group, which should, in theory, generate sodium cyanide (NaCN) when fused with sodium, thereby giving a positive Lassaigne's test for nitrogen.
• Glycine (NH₂CH₂COOH):
  • Glycine, an amino acid, similarly should generate sodium cyanide (NaCN) when fused with sodium, giving a positive result in Lassaigne's test for nitrogen.
• Urea (NH₂CONH₂):
  • Urea consists of two NH₂ groups and a carbonyl group, which should generate sodium cyanide (NaCN) and hence give a positive Lassaigne's test for nitrogen.
• Hydrazine (NH₂NH₂):
  • Hydrazine has a unique structure (NH₂NH₂). When it is fused with sodium, it does not readily form sodium cyanide (NaCN). Due to this unique property, hydrazine does not produce a positive Lassaigne’s test for nitrogen.
  • Hydrazine (NH2–NH2) have no carbon so does not show Lassaigne’s test.
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Hence, based on this re-evaluation, the correct answer indeed is  Hydrazine.