Question 1

Sodium nitroprusside has the formula $Na_2[Fe(CN)_5NO]$.

In this complex, the nitrosyl ligand is present as $NO^+$. When it reacts with the sulphide ion ($S^{2-}$) in an aqueous solution, a purple-colored complex is formed:

$[Fe(CN)_5NO]^{2-} + S^{2-} \rightarrow [Fe(CN)_5NOS]^{4-}$

In this process, the $NO^+$ ligand reacts with $S^{2-}$ to form the thionitrite ligand ($NOS^-$). Therefore, the ligand is converted to $NOS^-$.