In which of the following reactions conc. H₂SO₄ is used as an oxidising reagent?

An oxidizing agent reduces itself and oxidation state of central atom decreases.

2HI + H₂SO₄→ I₂ + SO₂ + 2H₂O

Oxidation state of central atoms:

HI = -1

H₂SO₄ = -6

I₂= 0

SO₂ = -4

Cu + 2H₂SO₄→ CuSO₄ + SO₂ + 2H₂O

Oxidation state of central atom:

Cu = 0

H₂SO₄ = -6

CuSO₄ = +2

SO₂ = +4

Hence the correct options are (ii) and (iii).