Sulphide ions react with `Na_(2) [Fe(NO)(CN)_(5)]` to form a purple coloured compound `Na_(4)[Fe(CN)_(5)(NOS)]`. In the reaction, the oxidation state of iron:
A. Sulphur, `Na_(4)[Fe(CN)_(2)NOS]`
B. Nitrogen, `Na_(4)[Fe(CN)_(6)]`
C. Sulphur, `Na_(2)[Fe(CN)_(4)NOS]`
D. Sulphur, `Na_(2)[Fe(CN)NOS]`