Which of the following statements are correct?
(i) S–S bond is present in H2S2O6.
(ii) In peroxosulphuric acid (H2SO5) sulphur is in +6 oxidation state.
(iii) Iron powder along with Al2O3 and K2O is used as a catalyst in the preparation of NH3 by Haber’s process.
(iv) Change in enthalpy is positive for the preparation of SO3 by catalytic oxidation of SO2.