248) Ozone when reacts with potassium iodide solution liberates certain product, which turns starch paper blue. The liberated substance is:

249) When KBr is treated with conc. H₂SO₄, a reddish brown gas is evolved. The evolved gas is:

250) A solution of a salt in dilute sulphuric acid imparts deep blue colour with starch iodine solution. It confirms the presence of:

251) By passing H₂S gas in acidified KMnO₄ solution, we get:

252) Reagent used in the qualitative analysis of group IV is: