Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen,

Nitrogen, sulphur, and halogens are covalently bonded in organic compounds. For their detection, they have to be first converted to ionic form. This is done by fusing the organic compound with sodium metal. This is called “Lassaigne’s test”. The chemical equations involved in the test are

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

$\mathrm{Na}+\mathrm{S}+\mathrm{C}+\mathrm{N} \longrightarrow \mathrm{NaSCN}$

$2 \mathrm{Na}+\mathrm{S} \longrightarrow \mathrm{Na}_{2} \mathrm{~S}$

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

$(\mathrm{X}=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$

Carbon, nitrogen, sulphur, and halogen come from organic compounds.