1. [Fe(SCN)]²⁺ 2. Fe₄[Fe(CN)₆]₃· xH₂O 3. NaSCN 4. [Fe(CN)₅NOS]⁴⁻

Answer: 1. [Fe(SCN)]²⁺ Key idea: When N and S are both present, Na fusion forms sodium thiocyanate, NaSCN, in the Lassaigne's extract. Na + C + N + S → NaSCN . With mathrmFe³⁺ it gives a blood red colour: mathrmFe³⁺ + SCN^- → [Fe(SCN)]²⁺ . Fe₄[Fe(CN)₆]₃ is Prussian blue, seen when only N is present. NaSCN itself is colourless. mathrm[Fe(CN)₅NOS]⁴⁻ is the violet colour with nitroprusside, for sulphide.

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

In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with Fe^3+ due to the formation of -

1. \([\mathrm{Fe(SCN)}]^{2+}\)

2. \(\mathrm{Fe_4[Fe(CN)_6]_3\cdot xH_2O}\)

3. NaSCN

4. \([\mathrm{Fe(CN)_5NOS}]^{4-}\)

Doubtly Asked 30 Oct 2026 NEET UG 2023 Practice test neet Save WhatsApp Report

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Answer: 1. \([\mathrm{Fe(SCN)}]^{2+}\)

Key idea: When N and S are both present, Na fusion forms sodium thiocyanate, NaSCN, in the Lassaigne's extract.

\(\mathrm{Na + C + N + S \rightarrow NaSCN}\). With \(\mathrm{Fe^{3+}}\) it gives a blood red colour: \(\mathrm{Fe^{3+} + SCN^- \rightarrow [Fe(SCN)]^{2+}}\).

\(\mathrm{Fe_4[Fe(CN)_6]_3}\) is Prussian blue, seen when only N is present.
NaSCN itself is colourless.
\(\mathrm{[Fe(CN)_5NOS]^{4-}}\) is the violet colour with nitroprusside, for sulphide.

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

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In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with Fe^3+ due to the formation of -

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