NEET 2025 · ChemistryPrevious Year Question

Which one of the following reactions does NOT belong to Lassaigne's test?

Answer: (B) $2 CuO + C 2 Cu + CO X_{2}$ . \textbf{Answer:} (b) \textbf{Solution:} Lassaigne's (sodium fusion) test detects nitrogen, sulphur and halogens in an organic compound by fusing it with metallic sodium, producing $NaCN$ , $Na X_{2} S$ and $NaX$ .

A. $Na + X NaX$
B. $2 CuO + C 2 Cu + CO X_{2}$ ✓
C. $Na + C + N NaCN$
D. $2 Na + S Na X_{2} S$

Correct Answer

(B) $2 CuO + C 2 Cu + CO X_{2}$

Solution & Explanation

\textbf{Answer:} (b) \textbf{Solution:} Lassaigne's (sodium fusion) test detects nitrogen, sulphur and halogens in an organic compound by fusing it with metallic sodium, producing $NaCN$ , $Na X_{2} S$ and $NaX$ . The reaction $2 CuO + C 2 Cu + CO X_{2}$ is the combustion/estimation of carbon (Liebig method), not a part of Lassaigne's qualitative test.

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