Question

Lassaigne's test for the detection of nitrogen will fail in the case of:

• A. $N{H}_{2}CON{H}_2$
• B. $N{H}_{2}CON{H}_{2}HCl$
• C. $N{H}_{2}N{H}_2$
• D. $C_6{H}_{5}NHN{H}_2.2HCl$

Answer 1

The correct option is C $N{H}_{2}N{H}_2$

Lassaigne's test is used to determine the presence of N in organic compounds. But $N{H}_{2}N{H}_2$ is an inorganic compound. No carbon is present in this compound thus, it will give negative Lassaigne's test.
In Lassaigne's test
$Na+C+N\to NaCN$
Thus carbon must be present for formation of NaCN which is further used in the test.