The reaction of nitroprusside anion with sulphide ion gives purple colouration due to the formation of

• Correct answer
  A

  the tetranionic complex of iron (II) coordinating to one $NOS^{-}$ ion
• B

  the dianoinic complex of iron (II) coordinating to one $NCS^{-}$ ion
• C

  the trianoionic complex of iron (III) coordinating to one $NOS^{-}$ ion
• D

  the tetranionic complex of iron (III) coordinating to one $NCS^{-}$ ion

Hence, the correct answer is option: 'A'.