HBr and and HI can't be prepared by treating conc. H₂SO₄with Bromide and Iodide as HBr and HI are strong reducing agents and they reduce H₂SO₄into SO₂ and themselves into Br₂and I₂respectively.

i.e.

2NaBr+H₂SO₄-----------_heat--------------> Na₂SO₄+2HBr

2HBr +H₂SO₄----------------------------> SO₂+2H₂O+Br₂

2NaI+H₂SO₄-----------_heat-------------->Na₂SO₄+2HI

2HI+H₂SO₄----------------------------> SO₂+2H₂O+I₂

Halogens have high electron affinity thus, they easily react with other elements to form compounds. They are just short of one electron to attain stable electronic configuration. Hence, there are not found in a free state in nature.

By the reaction of Hydrochloric acid and Manganese dioxide.

2HCl + MnO₂ --> MnCl₂ + H₂O + [O]

2HCl + [O] --> H₂O+ Cl₂

4HCl +MnO₂-->MnCl₂+ 2H₂O +Cl₂