Question

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

• A. $N{a}_4\left[Fe\right(CN{)}_{5}NO]$
• 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

Answer: (B)

$N{a}_4\left[Fe\right(CN{)}_{5}NOS]$

The appearance of a deep violet color upon addition of a few drops of sodium nitroprusside to SFE indicates the presence of sulfur.
Detection of sulfur: formation of violet color with nitroprusside

$\underset{\text{Nitroprusside ion}}{S^{2-}+\left[Fe\right(CN{)}_{5}NO{]}^{2-}}⟶\underset{\text{violet color}}{\left[Fe\right(CN{)}_{5}NOS{]}^{4-}}$