Lassaigne's test is used for detection of:

Lassaigne's test helps to detect Nitrogen, Sulphur, and Halogens in organic compounds. Here, sodium metal $\left(\mathrm{Na}\right)$ 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 $\left(\mathrm{Na}\right)$ into the ionic state. Lassaigne test reaction for sodium is given below:

$\mathrm{N}+\mathrm{Na}+\mathrm{C}\to \mathrm{NaCN}$

$\mathrm{S}+2\mathrm{Na}\to {\mathrm{Na}}_2\mathrm{S}$

$\mathrm{X}+\mathrm{Na}\to \mathrm{NaX}$

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