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Which of the following compounds fails to give a positive Lassaigne’s test for nitrogen?

1. Urea
2. Hydrazine
3. Phenylhydrazine
4. Azobenzene

Correct answer: Phenylhydrazine

Solution

In Lassaigne’s test, nitrogen is detected only if it is converted into sodium cyanide during sodium fusion. Phenylhydrazine does not give a positive test under these conditions, so it fails the test.

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