1. mathrmNa + C + N xrightarrowΔ NaCN 2. mathrm2Na + S xrightarrowΔ Na₂S 3. mathrmNa + X xrightarrowΔ NaX 4. mathrm2CuO + C xrightarrowΔ 2Cu + CO₂

Answer: 4. mathrm2CuO + C xrightarrowΔ 2Cu + CO₂ Key idea: Lassaigne's test fuses the organic compound with sodium to convert N, S and halogens into ionic NaCN , Na₂S and NaX. Options (1), (2), (3) are these fusion reactions. 2CuO+C→2Cu+CO₂ is the carbon-detection step of the copper(II) oxide test (Liebig), not Lassaigne's test. Option (4).

Topic: Qualitative analysis: detection of N, S, P, halogens· Purification and Characterisation of Organic Compounds

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

1. \(\mathrm{Na + C + N \xrightarrow{\Delta} NaCN}\)

2. \(\mathrm{2Na + S \xrightarrow{\Delta} Na_2S}\)

3. \(\mathrm{Na + X \xrightarrow{\Delta} NaX}\)

4. \(\mathrm{2CuO + C \xrightarrow{\Delta} 2Cu + CO_2}\)

Doubtly Asked 30 Oct 2026 NEET UG 2025 Practice test neet Save WhatsApp Report

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Answer: 4. \(\mathrm{2CuO + C \xrightarrow{\Delta} 2Cu + CO_2}\)

Key idea: Lassaigne's test fuses the organic compound with sodium to convert N, S and halogens into ionic \(\mathrm{NaCN}\), \(\mathrm{Na_2S}\) and NaX.

Options (1), (2), (3) are these fusion reactions. \(\mathrm{2CuO+C\to2Cu+CO_2}\) is the carbon-detection step of the copper(II) oxide test (Liebig), not Lassaigne's test. Option (4).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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

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