Lassaigne's test is used for detection of:

Lassaigne's test helps to detect Nitrogen, Sulphur, and Halogens in organic compounds. Here, sodium metal $\left(Na\right)$ is heated in the presence of the organic compound inside a fusion tube. The primary objective of this test is that all the available elements are converted by Sodium metal $\left(Na\right)$ into the ionic state. Lassaigne test reaction for sodium is given below:

$N + Na + C \to NaCN$

$S + 2Na \to {Na}_{2}S$

$X + Na \to NaX$

In the third experiment, $X$ can be anything such as $Cl, Br or I$.