Sulphuric acid oxidises hydroiodic acid to iodine and forms hydrogen sulphide and water.

Explanation

(a) The skeleton equation is written as `H_(2)SO_(4)+HI to H_(2)S+I_(2)+H_(2)O`
(b) Focusing on the oxidation numbers
`overset(+1)(H_(2)) (+6)(S) overset(-2)(O_(4)) +overset(+1)(H) overset(-1)(I) to overset(+1)(H_(2)) overset(-2)(S)+overset(0)(I_(2))`
(c) Locating atoms undergoing change in oxidation numbers
`H_(2) overset(+6)(SO_(4))+H overset(-1)(I) to H_(2) overset(-2)(S)+overset)(0)I_(2)`
(d) Determining the change in oxidation numbers

(e) Cris-crossing these changes in the oxidation numbers
`H_(2)SO_(4)+8HI to H_(2)S+I_(2)`
(f) Balancing the atoms other than hydrogen and oxygen
`H_(2)SO_(4)+8HI to H_(2)S+4I_(2)+H_(2)O`
(g) Balancing the atoms hydrogen and oxygen `H_(2)SO_(4)+8HI to H_(2)S+4I_(2)+4H_(2)O`