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In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with Fe3+Fe^{3+} due to the formation of

A

(1) Fe4[Fe(CN)6]3⋅xH2OFe_4[Fe(CN)_6]_3 \cdot xH_2O

B

(2) NaSCNNaSCN

C

(3) [Fe(CN)5NOS]4−[Fe(CN)_5NOS]^{4-}

D

(4) [Fe(SCN)]2+[Fe(SCN)]^{2+}

Step-by-Step Solution

When both nitrogen and sulphur are present in an organic compound, sodium thiocyanate (NaSCNNaSCN) is formed during the preparation of Lassaigne's extract. This reacts with Fe3+Fe^{3+} ions to form ferric thiocyanate, [Fe(SCN)]2+[Fe(SCN)]^{2+}, which has a blood-red colour.

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