NEET 2025 · ChemistryPrevious Year Question
Which one of the following reactions does NOT belong to Lassaigne's test?
- A.$\ce{Na + X -> NaX}$
- B.$\ce{2CuO + C -> 2Cu + CO2}$✓
- C.$\ce{Na + C + N -> NaCN}$
- D.$\ce{2Na + S -> Na2S}$
Correct Answer
(B) $\ce{2CuO + C -> 2Cu + CO2}$
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 $\ce{NaCN}$, $\ce{Na2S}$ and $\ce{NaX}$. The reaction $\ce{2CuO + C -> 2Cu + CO2}$ is the combustion/estimation of carbon (Liebig method), not a part of Lassaigne's qualitative test.
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