Question

A violet colour with sodium nitroprusside in the test of sulphur in an organic compound is due to the formation of:

• A. $N{a}_4\left[Fe\right(CN{)}_{6}NO]$
• B. $N{a}_4\left[Fe\right(CN{)}_{5}NOS]$
• C. $N{a}_3\left[Fe\right(CN{)}_{5}NS]$
• D. $F{e}_4\left[Fe\right(CN{)}_6{]}_3$

Answer 1

The correct option is B $N{a}_4\left[Fe\right(CN{)}_{5}NOS]$

The appearance of a deep violet colour upon addition of a few drops of sodium nitroprusside to sulphur lassaigne extract indicates the presence of sulfur.
Detection of sulphur: Formation of violet color with nitroprusside
$\underset{\text{Nitroprusside ion}}{S^{2-}+\left[Fe\right(CN{)}_{5}NO{]}^{2-}}\to \underset{\text{violet color}}{\left[Fe\right(CN{)}_{5}NOS{]}^{4-}}$