Lassaigne's Test (Sodium Fusion Test) is used for the qualitative detection of foreign elements like Nitrogen, Sulfur, and Halogens in organic compounds.

• Process: The organic compound is fused with molten Sodium metal. This converts the elements into water-soluble sodium salts:
• Nitrogen $\to NaCN$
• Sulfur $\to N{a}_{2}S$
• Halogen $\to NaX$
• The 'sodium fusion extract' is then treated with specific reagents (like Ferrous sulfate for N, Lead acetate for S, and Silver nitrate for X) to confirm their presence through characteristic color changes or precipitates.