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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
A
$[Fe(SCN)]^{2+}$
B
$Fe_4[Fe(CN)_6]_3\cdot xH_2O$
C
$NaSCN$
D
$[Fe(CN)_5NOS]^{4-}$
Explanation
When N and S are both present, $NaSCN$ forms and gives $[Fe(SCN)]^{2+}$ (blood red) with $Fe^{3+}$.
Detailed Solution
In case nitrogen and sulphur both are present in an organic compound, sodium thiocyanate is formed.
$Na+C+N+S\rightarrow NaSCN$
Which further reacts as:
$Fe^{3+}+SCN^-\rightarrow[Fe(SCN)]^{2+}$ (blood red colour)