Question

The covalent compound which does not give a positive test in Lassaigne's test is:

• A. 1,3-dinitrobenzene
• B. glycine
• C. urea
• D. hydrazine

Answer 1

The correct option is D hydrazine

Lassaigne's test is not given by compounds which do not contain $C$ atoms but contains $N$ atoms. For example, $N{H}_{2}N{H}_2$ (hydrazine), $N{H}_{2}OH$ (hydroylamine).
Since, these compounds do not contain $C$ atoms, so in sodium fusion extract, $CN$ is not formed and prussian blue colour is not obtained.