Which of the following statements are correct? 

(i) S–S bond is present in H₂S₂O₆. 

(ii) In peroxosulphuric acid H₂SO₄ 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.

HClO₄ is the most acidic compound.

Group number = 11 (Atomic number = 111)

Heavier element of p block do not from pπ− pπ bonds as their atomic orbital are so large and diffius that they cannot have effecitve overlapping.

The inertness of ? subshell electrons towards bond formation is known as inert pair effect. This effect increases down the group thus, for Sn,  oxidation state is more stable, whereas, for Pb,  oxidation state is more stable, i.e.,  is reducing while  is oxidising.