Question

A compound which does not give a positive test in Lassaigne's test for nitrogen is :

• A. urea
• B. hydrazine
• C. azobenzene
• D. phenyl hydrazine

Answer 1

The correct option is B hydrazine

Lassaigne's test is used to detect the presence of halogens, nitrogen, and sulphur in an organic compound.

Since hydrazine with the chemical formula($N{H}_2.N{H}_2$) does contain nitrogen, but it does not have carbon and therefore, the formation of $NaCN$ is not possible.

As $NaCN$, is not formed, Lassaigne's test is given negative. This is because the formation of $NaCN$ is a very important step in the reactions for the test of Nitrogen, sulphur, and halogens.